wha is the timing? on 1994 GMC Vandura 3500

when i goin the the hiway and is an slope , the speed go down drasticly from 65 to 35 mph., lus power..

Asked by for the 1994 GMC Vandura 3500
1 answer
sounds like a clogged cat converter. take it to a shop for a check to verify and a bid for repair.