powershop1804,
if it is cooling but just not enough it could be it has a leak and some of the refrigerant has just leaked out and it's lost it's ability to cool.
Normally in a case like this the system would be evacuated and refilled to insure you get the correct amount in it, over filling the system can cause problems that may damage the compressor.
So i would evacuate it, pull a vacuum and see if it has any leaks.
Then recharge it to the correct amount suggested by the manual you have for the truck based on its serial number.
That information i gave in the previous post was for the first serial number shown in the list from hypass, it may not be correct for your unit.

what is the serial number from your lift? i can check that and verify what it says for refrigerant capacity.