The hinge system on the poptop wears badly over the years.  If you examine
all the bearing points at the hinges in front and back and  some have
plastic inserts and some may not.  Using a lubricant that won't destroy the
plastic insert do your best to clean and lubricate these bearing surfaces.
The work in sliding friction rather than rolling friction so the more
pressure on the bearing surface the greater the resistance.   If you cut two
pieces of 3/4 inch pvc one about a foot long and the other about two feet
long you can use them as temporary props to raise the top.  Push the top up
directly, not by pushing on the bar in the front hinge system.  This takes
the hinges out of the equation.  Put the first tube in place to support the
top while you raise YOUR level with the obligatory cooler.  Now once again
push ON THE TOP itself and raise it one more foot placing the two foot tube
to suport the top.  Now you can use the bar to do the rest of the job.
Cosines kill your efforts when you use the bar only.  Ever notice how easy
it is once the top is almost up when using the bar on the unloaded top?
Cosines strike again.  In this case numbers don't rule but that mean old
trigonometry hampers your efforts.  Fizziks again, it's always just
fizzix...(adapted from Feynmann)