Over the summer I got a used 8.6" straight blade in a trade (no history on it). I installed the wiring yesterday and hooked the plow up on a 2004 Silverado 3500. It would not go up but I thought maybe something was frozen from being outside. I let it thaw out in the shop for a few house and it still wont pick the plow up. I can hear the motor running and if I push up on it it will go up just very slowly. It angles with no issue. My first thought is to change the fluid. It's full but who knows if it's ever been changed. What fluid should I use and what should I check over first to try and find the problem? thanks