Pab

there can be several issues about wheels spinning out of control.

I'm surprised after changing traction tyres with new ones it is still happening.
second scenario is, look at the wheels and see if all or particular the axle with rubber tyres is actually firm on the track itself.
Thirdly, earlier locos without load regulated decoders & motors had to go uphill at full speed to be able to reach the top and some of them never achieved this

locos on level sections should not be a problem at all unless you have such a heavy load behind the loco, the motor can't cope with it and the wheels are just spinning.

Your 37037 has had problems if its the same design as the BR 38, where as Märklin has added another set of wheels with Rubbertyres, first and last axle.
So you may write to Märklin and find out what they have to say or what they are going to do about it.

3170 has the same chassis as a 3179 (E 132) and the weight is not particular impressive so without a high efficiency motor and without a load regulated decoder this loco will not perform as well as pointed out with a digital conversion set (60903, 60923), actually this loco in its analog version is a very poor performer.
I also have the EP 2 (Primex , converted) and added another axle with rubber tyres.

Rubbertyres: When fitting new rubber tyres, make sure you understand and know the course why they don't work anymore.
putting to much load onto the loco will automatically result in wheels spinning (mostly analog version)
old rubber tyres get worn a.) because of the extended use over years, b.) dirty tracks, c.) over oiled engines, (rubber tyres hate oil).
With the latter experience you have the clean the groove as well to get rid rid of any sign of oil residue before replacing them with new ones, otherwise you are back to square one.
make sure you get the right size rubber tyres designated for this particular loco and also when fitting them make sure the rubber tyre is evenly distributed on the wheel itself and sits 100 % in the groove.

Good luck with your next mountain excursion.

regards.,

John

I believe this issue has nothing to do with the decoder or the efficiency of the motor. If the wheels spin,then power is obviously not the problem.
If a loco shows ths problem assuming that wheels and traction tyres are clean,upgrading it with a hyper-ultra efficiency motor and the latest top performance decoder will improve nothing,unless the vertical reaction on the tractive axles -in particular the one/s with traction tyres- is increased,or the number of traction tyres is increased (but this has some disadvantages,regarding costs -the wheels have to be swapped or a slot machined on them- ,current collection and track cleanliness.
That being said,there are some locomotives which are just too light or the weight distribution is so poor that they can not handle a heavy consist on anything but a perfectly leveled surface.

The "easy" solution is trying to add some weight to the loco, if possible at the areas where the axle with traction tyres are located. But this is not always possible due to lack of space.

I don't agree with all your assumption and in my opinion has nothing to do with facts.

A motor as described without a high efficiency system or a decoder that doesn't support the torque factor will struggle going up hill, as I've mentioned in my previous post unless at full speed.
To add weight to the loco is one option and as you've mentioned where needed, is not always possible and most the time impossible.

Having had a layout over 20 years and starting off with AC analog- digital and now converted all my locos with a 5 pole armature / perm. magnet, ESU lokpilots/sound decoders I can tell you and this is the fact my locos have very much improved going up hills.

Loco I've converted including the heavy SBB Ae 4/4 and BR E 44 had one set of rubber tyres and I've added another axle with rubber tyres (2 axles powered), It can pull any heavy train.

Another model I have is an american Steam loco weighing over 800g (loco only) but hasn't got rubber tyres and it pulls hardly anything.

To add another axle with rubber tyres does make a lot of difference and it is easier in the long run, if required, as to add weight to the loco.
One example is the BR 38.

Further more, an AC Analog motor may not support the extra weight or traction that is required

My explanation or solution, if this answer was directed to me,it is not one problem but the cause can come from different factors and to resolve it, some factors have to be combined.

regards.,

John

When wheels are spinning, simply there is not enough "friction" between wheels and rails; power (or torque to be precise) is enough, no matter if you have electronics and high efficiency motors.
The solution to the problem (apart from cleaning any oil and dirt) includes :
1) increase the weight of the loco
2) check the position of the wheels and the boogie to correctly distribute the weight (motorized boogie in rear position is better when going uphill)(we should talk about "isostatic" suspension of the wheels but seems too technical)
3) increase the friction (that what rubber tires are for)
So, if you can't increase the total weight of your loco, there are few possibilities to solve the issue.
Going back to electronics, "load regulation" is useful to start the train (electronics can increase the power/torque increasing the motor current, still keeping the speed) but not to solve the issue of wheels spinning (because more power means more slipping; on the contrary, should the loco stall with the wheels stopped, that would be a problem of "low power")
Have fun with your trains
Eugenio