Fuel vent clogged??

sounds like you have a bad gas cap

The cap itself is supposed to act as a check valve that only allows air to be sucked in, not vented.
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The charcoal canister should have 1 line from the tank and the rest to the intake for the gas fumes.

I took my Stant (not factory) gas cap off and it actually has a spring inside that allows pressure to escape the tank.

I don't know the specs on the escape pressure.

As you drive up the mountain atm pressure will decrease causing the symptoms you described.

You can remove the o-ring seal on the gas cap (don't throw it away). This will allow the tank to vent freely but might also allow fuel to spill.

Make sure the vacuum line to the charcoal canister is good.

Thanks for the help guys.

I replaced the stock cap with an aftermarket venting cap and am going to see if that helps(dont worry i kept the stock cap in case this one doesnt work)

Im also going to recheck all the vacuum canister lines. I replaced all the vacuum lines a couple years ago but ill recheck everything.

Ill let you guys know what happens

Is this the best resource for vacuum routing? This is what i used when i redid my lines. If so every thing looks correct.

Im going to pick up vacuum tester and test the valves on the canister see if its in proper order.

http://www.thumper300zx.com/z31/vacuum/vacuum.htm