1998 Chevrolet Blazer Movement

My Blazer will not move unless I floor the gas, forward and reverse. I changed the fuel filter and all sparks plugs are firing. I recently changed the transmission but after the radiator blew I had to have it towed because it kept over heating and shutting off. I replaced the radiator also. I'm all out of ideas so was hoping maybe you could give me a clue what to look for as an answer why there's no thrust anymore, it just kind of wont go!
I'd be MORE than happy to donate if you have the answer for me, be ecstatic if you have an answer lol.