changing gears between 3500 4200 rpm. accelerating barely pressing gas 2500 to 3100. i've done the tv cable adjusting many times. i've switched out the tach with my gt parts car. still exact same reading. unhooked the tach filter and jumped connections, same exact rpms no difference. can't use the on from parts car. wire broke off unless its ok for me to put a screw in it to make able to connect wire. what gives . it idles at 1200 to 1500. checked egr tube it fine. at 1500 it doesn't sound like its runnng that fast. sounds like 8 or 900. i'm lost. don't know if trans isn't right or tach. if take is wrong the trans is ok.

The tach gauge gets it's signal from the ignition coil, so you don't have to worry about anything being wrong with the transmission, for starters. There are several ways to check if the tach is accurate or not like driving at a known speed and recording what the RPM's are. Through a formula you can tell whether your tach is reading correctly for any given speed, but you'd have to know which axle ratio your transmission has. There were two ratios available in '85 so unless you know which one you have, you can't figure it out this way. You might get lucky and find either one of these two RPO codes on the sticker under the front hood on the driver's side wheel arch:

FW2 = 3.06:1 or;
F75 = 3.18:1

Have a look and post which one you see if you can find it. The other way to tell is by buying or borrowing a modern digital timing light and connecting up the sensor to any of the spark plug wires. The display will give you the actual RPM of the engine at that time. Then you can compare it with what your tach is saying. Good luck!