" Since the piston and seal were replaced and it stayed the same I am inclined to suspect the pressure relief valve."
Excuse me, but you are about to make the same mistake twice in a row.
There is a reason why I asked these questions:
How did you determine the lift cylinder/piston was bad?
Did you observe the oil leaking down from the top?
Did you check for a leaky pressure valve?
The point of tip # 16 wasn't to tell you HOW to fix the problem......but to tell you to DIAGNOSE the problem BEFORE you start replacing parts.
It's not that hard to pull an inspection plate & see if you oil leaking down from the top w/ a load on the arms. You wouldn't be the first guy to replace a cylinder in a bad piston. Or failed to detect a blown gasket w/ an internal leak.
If you do not see oil leaking down from the top, then test the pressure relief valve before you spend time & money to replace it. Because there are still other causes of the problem.