Chevrolet Forum - Chevy Enthusiasts Forums - 99 silverado 5.3 transmission acts like nuetral upon double down shift

Hi all
So I have a 99.5 1500 5.3. I lost reverse a few years ago. I pulled the trans and found a guy on craigslist to rebuild it. Yes I know I was taking my chances. He replaced everything broken at a good price. Sent me pictures and all. He worked for Monroe or something like that. They rebuild the transmission for autozone etc.
I got it back it put it in. again, like 3 or 4 years ago. It ran great, but I noticed that if I was on the highway doing like 45 and then stomped the pedal (causing a double down shift) the motor would rev out to like 5k RPM and then grab the gear, give a loud rev and a buck as if I popped the clutch. It still does that now. I drive the truck daily but just cant stomp on the gas too hard or it will do that. If I hit the gas so it only downshifts one gear its fine.
Im hoping this is an adjustment. If not, im not going to fix it. It has 225k. but im still curious

Thanks!