Conan

Car runs great, passed smog not too long ago, shift smooth and fine, except on the highway. Somewhere around 65-70 it seems to slip in and out of 4th if I barely touch the gas. It doesn't jerk or anything, i just see the RPMs fluctuate between 2500-3000 rapidly. Most of the search hits I have found talk more about slipping or shifting issues going into other gears, but mine seams to be only 4th. Any suggestions?

BTW, 208,000 miles.

fleetw00d

Is it really a 500 rpm difference, or more like 200 or 300? During normal auto trans operation, the output shaft of the torque converter does not spin quite as fast as the engine crankshaft because of the fluid coupling in the converter. The lockup torque converter in the transmission acts like a standard clutch and locks the converter such that the output speed of the converter is the same as the engine crankshaft speed. If it is working correctly, on level ground at highway speeds, the converter will be locked. If you acccelerate or start up a hill, the converter may unlock and you will noticec the engine speed increase by about 200 - 300 rpm (500 sounds like too much). When you back off the throttle or get back to level ground, you will probably notice the rpm drop by the same 200 - 300 rpm. If this isn't what it is doing, get it checked out.

Conan

I guess it is probably closer to 300. I just noticed that it seems to be between 2500-300, but looking more carefully on the way home (while still paying attention to road) it looks more like between 2600-2900ish. But it feels different than a few months ago. It seems like at a certain speed I give it gas and I can see the RPMs instantly go up 200-300 RPMs, without the car speed going up. It does seem to be doing what you are saying but I don't remember it doing this before, or maybe it's just jerkier than before? Thanks!