1985 GMC S-15 pickup shifts into overdrive early
I've just purchased a 1985 GMC S-15 "Sierra Classic" pick-up, and the engine and transmission has supposedly been rebuilt about 7 years ago, but the vehicle has been sitting pretty much since then. The truck runs good, and shifts just fine from 1st through 3rd gears, but will not shift into the overdrive gear until about 57 mph on secondary roads, and is horrible on the interstate...If Im doing 65 mph on the interstate, and encounter even a mild grade, the transmission shifts down into 3rd gear, and the engine, I assume is spinning around 5500 to 6000 rpm...NOT NORMAL! I've already adjusted the TVI cable per the manual (Haynes, and internet instructions), and am convinced that it's NOT the TVI cable... There are a couple of connectors hanging from the firewall that I have no idea where they go, as well as a few open vacuum ports (two from the "can"). As you probably know, the Haynes manual is not much help as far as wiring and vacuum diagrams, so Im basically stumped here....I HAVE to have a way to work, which is about 72 miles of all interstate, and I simply can't keep running the truck at 6000+ RPM whenever I encounter a slight grade....She seems to run in the overdrive gear just fine as long as Im on level ground, at 65+ mph, but once the vacuum increases from the incline, she kicks down into 3rd. If I let off the accelerator, she will then shift back into overdrive around 57 mph....If ANYONE can help me with this problem, I would deeply appreciate it...I just feel its something to do with the vacuum input to the transmission...This is URGENT, so please call me with any ideas...1985 GMC Sierra Classic 2.8 liter V-6...automatic transmission....Please call "Mark" at (404) 444-6077...again, I appreciate any help before I blow this engine up!!!
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Nevermind, taking truck to AAMCO....says he is familiar with the truck and transmission and guarantees a fix by repairing or replacing the valve body...maximum cost is $375.....Seller says he'll pay half.....