So I have an 85 k5 blazer with a 700r4 tranny. My transmission won't engage in reverse and when its in neutral it drives forward when i let off the brake. All the other gears work as well. I put it in reverse and apply the gas and it will rev up to low rpm and same for when it' s in park. I checked the linkage and it was fine and engages in all slots.

Before this issue when i was driving it would rev really high in between 1st and 2nd gear and even in other gears and would have trouble shifting. and when i would try to go in reverse it would either rev up really high rpm and take a while to slowly inch backwards or just inch back and than pick up speed and when i would stop after it gets up to speed in reverse i could go back at normal speed.

I've also had a transmission leak in the cooling line for a long time before this issue and still have it but where the leak is it solidified to a pick gum texture but still leaks regular looking fluid.

Can someone please give me some feed back on what is wrong and what I should do.