Car won't shift.
 

I have a 2000 Chevy blazer, 4-wheel drive v-6 and I blew a tranny two weeks ago. My friends and I put in a new/used transmission. When my tranny blew I could only go into drive, shifting seemed loose and I had high RPM's. Well we put the new one in and now no high RPM's, shift has tension at the wheel but my car won't go anywhere. I can hear the click when it shifts but I press the gas and RPM goes up as normal. What should I check on to make it shift? Please help.