I have a 91 firebird 3.1L V6 i have 2 problems...
1) if im stopped on a little hill and start to press on the gas the car tends to jerk at first then goes, this happens in first gear, but i thought i noticed it in second gear also... it kinda feels like something is up with my tranny..

2) When im on the freeway and i go about 70mph my car starts to shake but once i get to 80mph or under 70mph it stops shaking....

 

I'm not so sure about the first part, but the 2nd part is due to your tires. How old are they? When was the last time they were balanced? Could have possibly thrown a weight. Get your tires rebalanced and while it's in the air, have them check for play in your idler arm, wheel bearing, and tie rods.

 

1st, check your tps, adjust it accordingly.

2nd, bad tires, tires out of balance, alignment, bad front steering parts.