1994 4.3L trans+4wd problems need advice

My 94 s-10 4.3L chevy blazer automatic with overdrive is stuck in 2 wheel drive now but was stuck in 4wd low when i got it , the light on the swith inside the vehicle is not burnt out becuase it comes on when the ignition is turned, but then goes off and doesn't work it will not engage the 4wd. I thought it could be the vaccum swith on the transfer case but i couldn't get the old one out to replace it so i just disconnected the switch and it put itself in 2wd. Other than that I really have no idea what to do, which lines should i check and what else could be cuaseing the problem. The other problem is that when i am driving and get the car to 30mph you can push the gas as hard as you like, but the engine just revs and it doesn't go any faster.No check engine light has come on. I think it is the trans, but then again i don't know. please any suggestions would be much appreciated. thanks

Have you checked your transmission fluid level with the engine running yet?

My 94 s-10 4.3L chevy blazer automatic with overdrive is stuck in 2 wheel drive now but was stuck in 4wd low when i got it , the light on the swith inside the vehicle is not burnt out becuase it comes on when the ignition is turned, but then goes off and doesn't work it will not engage the 4wd. I thought it could be the vaccum swith on the transfer case but i couldn't get the old one out to replace it so i just disconnected the switch and it put itself in 2wd. Other than that I really have no idea what to do, which lines should i check and what else could be cuaseing the problem. The other problem is that when i am driving and get the car to 30mph you can push the gas as hard as you like, but the engine just revs and it doesn't go any faster.No check engine light has come on. I think it is the trans, but then again i don't know. please any suggestions would be much appreciated. thanks

You said that when you got it, it was stuck in 4 wheel low. Did you ever get it out of 4 wheel low or just disconnect the vacuum switch. Disconnecting the vacuum switch just disengages the front axle. If it won't go over 30mph, it might still be in 4 wheel low. Try disconnecting the battery for a couple of minutes to reset the transfer case control module and reconnect the vacuum switch. then see which range you're in.

yes i checked and replaced all fluids, and it wasn't haveing the trans problem until i changed it. It excelerates fine the problem occurs while your driving and you slow down to around 30 and then try to excelerate again.The engine will rev higher but not exceleration occurs. however, if i come to a complete stop at a light or sign it excelerates fine. so basically the trans problem only happens when driving.