Brandan K. Sites

I have a 99 5.7 suburban, bought it off someone back in Feb it has 244,000 on it, 2 days ago was a far distance away from home, went to eat when I got done, got in it started it and went to back out but no reverse (was sitting on a hill and it still wouldnt move was like something was keeping the whole thing in 1 spot) so had to use nuetral, then 1st is barely to not even working, when I start it it shakes for a bit then stops, it would bogg down when you stomped it now it doesnt, and when your in drive and push the petal to the floor it doesnt even downshift. It has the 4L60E in it, im tore between if its the transmission going bad or something else. Help please?