Engine over-revving until it shifts into 3rd gear then its back to normal

I have a 1994 Chevy S-10 Blazer. We had some snow here last week and I used the 4WD. A couple of days ago I noticed that the engine sounded like it was over-revving and not pulling as fast as the engine sounded. It is acting as though it is stuck in 4WD low. As I gain speed and the transmission shifts into third gear the engine rpms seem to catch up and the engine speed is back to normal. It pulls as it should. I checked my tranmission fluid and it was a quart low. I topped it off. That did not change anything. I disconnected my battery for 15 minutes and still no change. I changed the plugs, Dist. Cap, and Rotor--no change. I am at a loss in this matter. I have read through the forum and I am thinking two things---one: replace the tranmission filter and fluid and a possible bad TPS. Any suggestions are welcomed and appreciated.

mine was doing something like this last time I used 4x4 . In my situation , the vacuum switch needs replacing on the top of the transmision/transfer case. It is allowing tranny fluid to be sucked out of the case and into the intake manifold . It fowled out one of my plugs where it was burning it . I get blue smoke when I shift to 4x4, That was my big clue. I am not sure where you could check for fluid since mine has been well modified with carb . I was losing a couple of tranny quarts every 100 miles or so. Just a thought . Rob

Get a new filter in it ASAP.

I want to give everyone an update. I just changed the fluid and filter in the transmission. The old filter was extremely loose and almost fell out. I replaced the o'ring and filter and it was quite a lot tighter. The fluid did not smell burnt but it was a brown color. I checked all the vacuum lines for the FWD system and they seem to be good. I check the lines under the battery and they do not have vacuum until the vehicle is put into 4WD. I am assuming this is correct? I can hear a click on the passenger side of the vehicle when I put it in and out of
4WD. Here is the kicker--the problem is still there. And now I have an update. If I start driving with the vehicle cold it seems to start out in a very low gear and when I get up to about 35 to 40 mph it seems to go straight into a high gear (or the gear it should be in naturally). But if I let it warm up until normal operating temperature it starts driving in the gear that it should. Thank you for all your suggestions up until this point. Any further suggestions is appreciated

Just remember that your torque converter will not lock up until the engine is warmed up.

I took it out on the highway tonight for about a 20 mile run. It seems to be getting better. The real test will be in the morning when I drive it to work. I'll see what it does then and then I'll post a reply. Just a question to BlazerLT--in the past it never had to warm up to start in the right gear ratio. So why now? Thanks for the input.

So again what is it exactly doing and what gear is it hanging in?

The problem is still there. When I start the vehicle and put it in drive to drive away the engine rpms are real high and the vehicle moves real slow. I can give it gas (alot) and the engine sounds like its in 4WD low. The when it shifts through 2nd gear and almost into 3rd the engine rpms drop and the vehicle pulls like it should. Its kind of hard to explain.

Sounds like your tranny is shot bud.

Sorry to say, but I'd have to go along with BlazerLT, it's toast.

That or the tranny filter is clogged.

Sorry to hear this. I am taking it to a transmisssion place on Friday. I'll let everyone know the results. Thanks for all the inputs.