Mark lift MT40G scissor lift weak forward driving

Hello New member, have used lots of advice off of here a lot of knowledgeable members...so here I go. I bought a very used mark lift MT40G all terrain scissor lift 1800 hrs...runs good, lifts good, reverse hesitates but moves ok, forward may not move and when it does stopS or is jerky even on very flat ground and even reverse does a little. Checked tow valve operates same way whether on or off ...?? Hydraulics are not my thing but curious to hear from others who may have scissor lifts . Thanks