1998 Chevy 1500 Transmission Question

Hi Group, long time, no see. I hope all is well with everyone.

The situation is this: I just picked up a 98 Chevy 1500 Z71 pick-up with a 350 Vortec and I may have a transmission issue. When I start out driving in the morning the truck runs and shifts fine until I hit top gear (OD). Then I feel what I think is a little slippage. The tach will jump a small amount and the tone of the engine will change. This only happens between 45 and 55 mph (around 1200 to 1500 rpm). If I keep it in 3, not a problem. If I set the cruise, no problem (1500 rpm @ 55 mph).

The trans fluid level is right on the mark and does not smelled burnt. I was told new plugs may solve the problem, not quite sure how or why.

Any help, as always, is appreciated.

Thanks, Mike

GottaSki wrote: a misadjusted brake light will cause the TC to unlock and lock with each flash, because its supposed to unlock when you hit the brake.

How is a torque converter affected by anything electrical? Last time I looked a torque converter was a purely mechanical device.

it should be a 4l60e, which lock up is controlled by a solenoid, the converter actually has a clutch plate that locks the engine to the trans, if its not the sloenoid you may have a problem in the converter or whatever feeds the converter oil.
usually the check enf=gine light will come on possibly if electrical, take to a good trans shop and have them plug it in

Thanks guys!

take it to a place that hooks it up to the cooler lines to flush the entire system including the converter. if you pull pan you can usually only get 4 quarts out and it is a 9 qt. system

also go slightly faster and see if you still have the same issue. Sometimes people will cruise right at the point it engages and it will engage and disengage and make you feel like there's a problem.