the transmission in my 96 Silverado 1500 and now the speedometer doesn't work nor does it gear shifter light up

Hello, clearly something was disturbed during the transmission replacement. It could be a wire that is pinched or not reinstalled properly. There's no guessing to be done here, tracing the circuit that is related to the parts not working is needed. Of course, check all fuses in case one or more is blown - but you'll need an owners manual or workshop manual to show the fuses and which ones are which. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops