Hello, first time posting in forum- I've run into a pretty scary issue as I just bought a 2000 silverado 1500 LS z71 5.3L. I bought it used and guy didn't do much upkeep with fluids as I changed oil, oil filter, transfercase fluid, front and rear diff all with oem fluids except for tranmission i used dexron vi / mercon lv by valvoline. When I bought it he mentioned a flutter around 40-50 and it shifted fine when i drove it home. So after changing the tranmission fluid, seal, and filter my truck now revs super high and doesn't shift. First test drive after changing the fluid and letting it run for 30 minutes after i added 5 qt into the trans dipstick where i saw on youtube to add it. and it drove fine but then after 3 minutes or so of driving it almost felt like it has 1st gear but i'd hit the gas and it wouldn't engage into the next gear. I kept checking fluid then added another 2 quarts the following day and let it warm up and now the fluid is still low. when i let it drain when changing the fluid i noticed a small black tab ripped by where the seal goes but other than that everything else looked fine. Park, reverse, drive, N, 3, and 2 all engage fine and the truck takes off on its own when putting into drive but soon as i try to drive and leave my driveway it just revs high and doesn't really move, im afraid to rev it higher to see if 3rd works but im not sure what it could be? should i add more fluid because i let it drain overnight? when i drove it the mornig after i added the first 5 quarts i drove it hard and was driving fine but then after that seems like everything went downhill i also hear a tiny squeek from when i hit the gas and sounds like a light ticking noise by the oil pan/ transmission area. No check engine codes only codes i have on my scanner is abs motor freespins. Like I said i just bought the truck so idk what to do i dont have money to put in a new transmission. one thing i did notice when i bought itwas the cigarrette lighter fuse was blown so OBD2 port wasnt working to i put in a new fuse he installed aftermarket lights on it im assuming blew fuse. I can upload a video of it if needed to help diagnose i spent every dollar i have on this truck so im hoping for a miracle. Hope its a fuse or do i have to reset tcm after fluid change? transmission was shifting ok before fluid change, could i have him the pan with something i was struggling to get it off