Depending on what kind of "struggle", it could be electrical. While newer, our fifth wheel required replacing a 40 amp "self healing breaker fuse thing" with 80 amp or above. Otherwise, we'd get movement, then would stall, then move again, then stall.
Also, bear in mind that these slides draw some power to move that much weight. It could be that having a bigger battery bank could be part of it. (Even if hydraulic vs. electric slides, they still use DC current.) More batteries increases the available amps and current. (Or something equivalent, the electricians here will correct me!)
2018 Grand Design 399TH (44') • 2109 Ford F-350 Dually
With 2016 Harley Heritage • 2013 Sportster with a sidecar!