uphill shudder in automatic 4th gear

Hi, I've got a 93 GP, ~95K miles, 4sp automatic transmission, fuel injected, 3.1L V6, generally runs OK. It just started shuddering/stuttering on medium uphill grades, only in 4th gear around 40-50 mph. 3rd gear is smooth and shifting between gears is smooth as well. It will shift into 4th on the grade and start to shudder right away; it also will shudder if I enter the climb already in 4th.

Any ideas? I plan to have it serviced but want to make sure I can explain it OK to the mechanic.

could be a converter slip or 4th could be slipping, also it could be a engine problem do to the fact your really starting to load down the engine in 4th

New plugs and wires cured that on my mother's Buick.

Try having the transmission scanned with a trans capable scanner. Sounds like the Torque Converter Clutch Solenoid to me. Will cause shuttering due to not engaging and disengaging properly.

Thanks for the feedback.

Two developments: the problem spread to other gears, and then the engine very suddenly began to sound like it had a serious exhaust problem. (i.e. it sounded like a Harley Davidson). The mechanic found one spark plug had become disconnected, and expects new spark plugs to resolve the issue.

Make sure you use quality OEM style plugs, no fancy schmancy multi-electrode Bosch junk!!! I'd put a new set of wires on her too while you're at it.

Back in shape!

Installed new spark plugs, and both problems (shudder and loud exhaust) are gone. Plus the mechanic used non-fancy-schmancy plugs (The old ones were Bosch). Thanks!

Thanks for the feedback. We like hearing happy endings.

I had a vehicle w/120K do the going up a grade OD shudder...fluid and filter change fixed it.