Slideouts Stalling

The battery is probably the culprit in this case. If it's old it may be weak and unable to deliver the steady amperage required to operate slides. Even with shore power on the converter in most RVs deliver from 6-10 amp/hours of charge to battery which takes maybe 3-6 hrs to completely charge the battery. The battery depending upon its reserve capacity has to be able to allow maybe 20-30 amps to operate the slides therefore drawing down on a weakened battery with the amperage required to operate slides cannot be compensated even by having it connected to shore power. Most good or new batteries can deliver their full amperage for whatever the reserve capacity is at 12V without a drop in this voltage. As the amperage is increased the voltage will fall on a weak battery which causes it to heat because of the required amperage demand. If this be the case your slides will move slowly. The other issue is the current through your slide motors will be less causing them to get warm or heat up which is not good. Sounds a little technical but in another life use to be an electronics person.)