We went to use the Blazer this morning and when I went to put it into reverse it did nothing. No grinding nothing at all. when I put it into reverse it makes no noise at all it's like being in nuetral So I pushed it backwards out of the driveway so I could check out to see if drive worked. So I put it into drive and it started to go then I noticed that it was not changing gears. It was staying in low gear. I kept going with it and then it decided to change gear. but as soon as I lowered the speed it would go into the low gear and it would not come out again. Then I played with the gas and got it to shift gears. So no reverse and drive gears are not shifting good at all. any ideas as to what would be causing this ?. Before this morning we had to problems with the tranny. We used the blazer all day yesterday and it worked great. I checked the tranny fluid and it's full.

 

It sounds like you have a fractured sun-shell in the transmission which would result in no reverse, 2nd, or 4th.

If that is the case, then the transmission doesn't need a complete rebuild, but it will need to be removed and gutted to replace the sun shell. I recommend the 'BEAST' sun shell as relatively cheap insurance against failure.