The center pedal is a " parking" pedal . When the engaged , lever is to the left , it bypasses fluid around Travel Control Valve, normally used to help warm transmission drive fluid on cold days, just start engine , leave engaged for 5min or so , then disengage by swinging park lever to the right ,allowing all fluid to the Travel Control Valve. I also bought a 1550 that had set for several years, had the same problem (slow travel, stall early at hard push). What I found was that the park lever would swing left and right ,but was not actually moving the linkage to the Travel Control Valve fully as it should. Remove floor plate, follow the linkage down to tcv, move park lever and make sure everything is moving correctly...( pretty well self explanatory when you look at it) mine was an easy fix, just a few squirts of Aerokroil penetrating oil and working lever left and right until everything moved freely,allowing all fluid to the TCV . Also. move antistall lever (T handle top left corner of dash) in and out and watch linkage , also connected to the TCV, it pushes in and pulls out but moves only app 1/8 - 1/4". These are very good machines and once familiar with it you can grade within 2" of an object with confidence. Hope this helps.