I can think of a couple of causes… 1. trim relay can burn the contacts so that they wont carry much current. Enough at idle, but under power it takes some current to run the pump against the pressure of the motors thrust… 2. pump itself, which includes the rams. Could be leaking o-rings, or the pump itself could be bad or have a bad motor that cant produce enough pressure… This assumes that you are actually able to move it upward, just not at decent power level settings…2008 Pantera Classic2014 Mercury Pro XS 200