Theodore Pendergrass

Hey guys first time here and first time posting. I have a 2004 chevy 1500 4x2 automatic 5.3L with a 4L60e transmission. I had just replaced my transmission, everything went it smoothly started up great. As I went to put it in reverse I had to rev it up in the 2000 to 3000 rpm in order for it to back up. I put it in drive and it took off with no problem but wont shift out of first. As I drove it in first once I let off the gas it wouldn't go any faster or kick back into first until I slowed down to 5 to 10 mph. It wont shift manually either just stays in first gear. Is there something I did wrong. I'm thinking the torque converter got taken out of seated but it wouldn't go into any gears if it did right or wrong. Any and all help would be great thanks guys.