The slide motors stop when they sense a certain current draw which they interpret as the slide being fully open or closed. I would look at lubrication on the slide rails, or even dry seals adding to the resistance.

Another concern would be the coach not being level adding additional tension/resistance as it tries to move.

Have you tried having someone trying to push the slide in while engaging the motor? Our friends have an 03 that had not been lubricated properly before they bought it and they could only get the slide to retract with manual help. Once all the old grease/dirt was removed from the rails and properly lubricated it started working as expected.

There is always the possibility the motor is failing, but I would exhaust all other items before thinking that direction.