If you see any tracks or gears along or under the slide, start with those. Personally I use a dry lube, but I'm sure like everything else, everyone has an opinion on what's best. Have you lubed your slide seals as well? 303 protectant or something similar works well for that. If lubing everything up doesn't do the trick, check your batteries. Slide motors draw a lot of power. A sub par battery will cause issues.
Cut it 3 times and it's still too short...
2017 Sandpiper 381RBOK
2006 Ram 3500 Cummins Dually