I have a 91 Z 350 and when i am on the highway go 70 my RPM is at 3500 what would cause this problem and it got 2.77 gars

 

what size tires do you have? is it in overdrive or staying in 3rd gear?

it could be that your stock tach is broken or off

 

My tires size are 17 and yes is in overdrive

 

Sounds like you have joined the club of faulty tach owners. Mine reads 300 rpm high at idle and pegs 7k when it's actually below 6k. There's a fix on the boards somewhere.

 

Do you now have a V-8, in an original six cylinder car? Can you feel the TCC lockup? Have you been lied to before?

 

i had a 305 and now i have a 350 tpi no i dont feel the tcc lockup

 

Is the four wire plug actually plugged into the trans?

Does your engine warm up properly? What thermostat do you have installed?

How many miles on the trans? Fluid full, and pretty and pink?

Do you have another tach (hand held, tach/dwell meter) you can hook up, and see if your tach is accurate?

 

1) the four wires on the trans i dont no but i will check on that
2) Yes it warm up properly and the thermostat is 185
3) the tran gots about 10000 mils on it and yes the fluid is pink