I have a 94 GMC Jimmy 4.3 4x4 and it seems like I have lost my overdrive. I had to drive 100 miles to report to drill for the National Guard and I was putting out about 3000RPM at 70-75mph on the highway. Of course my gas mileage sucked.
What the heck has happened? Could it just be a sensor? I do not have a check engine light. Might this be an easy fix (please tell me it is!)

Mike

 

Well I guess to start this off would be how much fluid do you got in the tranny and what color is it?

 

time for a rebuild most likley the 3-4 clutchpack is prolly smoked

 

I got the xmsn rebuilt. I was starting to lose 2nd and 4th. It cost me $1600 but atleast it's fixed.

Mike

 

It could just be the torque converter lock up clutch. One of the sensors in early 4L60Es was in a hole that was too big for it and would let fluid seep past, telling the computer not to lock up the clutch in the converter. This happened to my 1997 C1500 with a 5.7 Vortec and a tranny shop installed a fix that made it last for another 50,000 miles. The truck had 204K on it when it got the fix.