Overdrive out

I have a '95 Chevy Cheyenne with a Vortec 4.3 liter V-6. It currently has 160,000 miles. The truck is in really good shape and runs excellent until recently. I just had the ignition switch changed, and the module
on the distributor changed. The faulty ignition switch was keeping the speedometer and tachometer from working. They sat at 0 even while giving gas. It also caused my maint req'd light to come on. The truck also did not start in first gear from a stop. The switch kept the transmission from working correctly electrically.
After getting all this repaired the truck seemed to run fine until I noticed that it was not going from fourth gear and settling into overdrive at 50 mph. From driving the truck I can tell by sound of the engine, and revolutions on the tach, that I am running way too high rpm's for say 70 mph for example. I brought the truck back to the mechanic and told them that it was not going into overdrive, and he checked over all the work that he had done, and told me that he feared it was an internal problem.
After taking to get another opinion they say that it is an internal problem as well. I have been driving the truck around for about 3 months now with the diagnosed "internal problem" on the tranny with no other problems but higher engine revolutions and less mpg's. I am about to get it overhauled, but wanted to know if it could possibly be an electrical problem, and not a mechanical problem with the transmission at all.
If anyone could offer some advice/ knowledge/ information before I sink some big bucks into getting this transmission overhauled I would greatly appreciate it.
Thanks, Jonathan
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This needs to be scanned on a trans capable scanner to confirm the o/d shift solenoid operation and tcc operation, if the electronics in the unit check ok, it's coming out.

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Jonathan wrote:

transmission overhauled. It may not go into overdrive when it's overhauled. Now are you sure you mean overdrive or the lockup torque converter? If the engine is low on power or the transmission module senses low power for some reason, it will not lock up and go into overdrive either. When you are talking about this much money, diagnosis is the key. Since you are driving OK, I'd look for a third opinion.
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(should be same trans in his truck). At 55mph & on a level road & level accelerator, it turns like 1600 rpm IN lockup mode and 1900 rpm OUT OF lockup mode--both scenarios IN od. I don't think he'd notice approx. 400 rpm difference due to lack of lockup at 70 where he describes it as "way too high rpm's for say 70 mph". He must be noticing the lack of overdrive, approx. 700 rpm difference ( At 70 & NO od, mine would turn ~ 2400 rpm; at 70 & IN od, it'd turn ~70% X 2400, or about 1700---a difference of ~700 rpm: both IN lockup. Both trannies have a 70% od gear-reduction.). I think your thinking and mine are in synch--a loose wire? poor connection? defective solenoid? blown fuse?!?! Something simple to be pinpointed NOW via a proper scan would be much cheaper than an unnecessary rebuild and THEN finding that poor connection. Luck to you, Jonathan. Pay attention to Al & Shep & find the simple solution via a 3rd opinion, or 4th. Too coincidental that your od quit right after you had the ign. switch and distributor module work done. I don't think your trans needs a rebuild just now! s
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Hey, thanks alot you guys. I am definatly trying to get lined up with an allison certified repairman(even though I know mine isn't an allison) I am going to ask him to run the electrical checks ya'll are talking about before I drop 1300 benjamin's. FYI: My truck usually runs at about 1600/1700 rpm's at 70. Now at 70mph they hold at about 2000/2100. As I go up hill they increase with out downshift to about 2400/2500. I really appreciate all the advise, and I will keep in touch with anything that the repairman tells me.
-Jonathan
sdlomi2 wrote:

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