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89 3/4 ton Silverado

Hey group.....its been a while since I've bothered you people...My truck has been running perfect for almost a year now(thanx to you all).........Problem....truck has an automatic trans with overdrive.......at cruising speed of 55 to 65mph...in overdrive it acts as tho its trying or wanting to shift into another gear........at 70mph or higher it seems to stop.......Its not a cutting out or misfire....and it doesn't seem to happen in (D). Could this be a vacuum problem??Any help is mucho appreciated......................nailgunner

Reply to
nailgunner
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overdrive.......at

3 or 4-speed automatic? Does it act like it's trying to upshift or downshift?

Doc

Reply to
"Doc"

sounds like TCC hunting on-off-on-off............

does it have a tach ?

if so, how many RPM's is engine speed changing when it does this ?

Reply to
Gary Glaenzer

That's what I thought; were the 400's more common on the 2500's than the

700's?

Doc

Reply to
"Doc"

Reply to
nailgunner

It's doesn't use vacuum, just the TV cable. TH350's use both vacuum and a kick-down cable, TH400's use just vacuum. Are you sure it wasn't the tranny vent hose you found?

Doc

Reply to
"Doc"

Reply to
nailgunner

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