ok let me start off by saying I'm not an expert with transmissions, especially automatics... but I do know I'm having a problem.

vehcile: 1991 Camaro Z28 350 5.7L 700R4 3:08 Rear Gears.

Taking off from a stop it drives and shifts normally through 4 gears and seems normal. However crusing at 80km/h (50MPH) in OD this car holds at a constant 2400rpm which seems awefully high to me.

In comparison, my IROC with a 5 speed and 3:45 rear gears cruises at 1200rpm at the same 80km/h.

Is the torque converter not locking up, or what could possibly be the problem? What can I check or look into?

Any help would be appreciated, thank you.

Sounds like your maybe on the right track. I have a toggle switch that controls my converter lock up and the rpm u stated is about where mine runs at also when I have switch off. Check the square white plug down at trans for damage or if its even plugged in first

ok thanks, I'll check into that first thing in the morning.

I put my switch in cause if you wanna get it on with someone you dont want your converter coming in at 35 mph and killing your acceleration. TCI tranny compnay even recommeneds it as option with trans they sell so its ok to do just wanna def use on highway so not to overheat tranny but stop and go driving the converter really takes away from the cars fun

It won't if everything is working properly. The ECM will unlock the TCC under low vacuum and high throttle opening.

the converter unlocks also when u apply the brakes and is how TCI tells you to over ride its function by installing a switch there by tricking the ecm into thinking the brake is always applied until u turn the switch off returning normal operation

That's now how it works. The ECM doesn't know when the brakes are applied. The brake switch interrupts the +12v source to the TCC solenoid directly.

Regardless, you don't need it if your ECM is working.

ok I have two plug-ins on the tranny that I can see, neither are white. One is a three wire plug near the shifter linkage on the drivers side, and one two wire plugin at the tail end of the transmission.

both plugs are in and appear to be in decent condition. looks like I'll have to dig in my shop manual and see what information is in there.

any other advice?

The 3 wire plug (with 4 "prongs" if you unplug it) is the TCC connector.

Are you sure your tach is accurate?

no I am not sure my tach is accurate, but a problem certinally exists. I can drive my heavily modded 5.0L 5-speed IROC to work and back 4 days on a 1/4 tank of gas, and my stock 5.7L 700R4 will burn 1/4 tank of gas in one day.

I realize the gas tanks may be different sizes, however they both cost approximatly the same amount to fill up.

ok I just thought I'd come back and update this...

I found a leaking vacuum hose and replaced it, the tranny now shifts properly. I also found my tach is very inaccurate, VERY. Lastly I reset the timing, which was set to 0.. I've now got it set to approximatly 7deg and it runs much better.

With the above problems resolved, the gas milage has greatly improved - as well as increased performance.

A quick check is while in OD you should read 1000 rpm's @ 40MPH.