About two thousand miles ago my '98 4dr 2wd a/t Blazer started having shifting issues. I would be on the highway and get up to ~55mph and it wouldn't shift into the next gear. If I gave more gas the RPM's would quickly elevate to extreme levels. So I pulled over and rested the car, got back on the highway, problem went away. A thousand miles ago it did the same thing briefly on the highway for about a mile then went away. Fluid levels aren't low. Couldn't really tell if the fluid is good or not, the Express Oil Change place said it was brown. Though they also told me my fuel filter needed replacing and I had just replaced it 500 miles ago. So what does he know.

I bought the car at 80k miles. It is currently at 120k miles. So I don't know if the previous owner changed the fluid already at something like 60k to 80k. I'm wondering if its something as simple as I need to flush the fluid and change the filter? Or does this issue sound like something that would warrant a rebuild? Any other common issues with easy fixes would be great.

Kinda a bigger picture. I don't put a lot of miles on my car. I've had it for 9 years and only put 40k on it. If the solution to the above issue is something simple, how long does the tranny/engine typical stay good for? If 160k miles is no issue that would be great, I could get another 5 years out of this car.