transmission on 1992 Cadillac Fleetwood

i borrowed my sons car so i have limited info. the trans seems to slip but run well occasionally, when it is in low gear the dash speedometer reads zero and wont move any higher than second gear, when the speedometer is working , usually after car has sat for a whilethe trans and the dash work for a few miles

Asked by for the 1992 Cadillac Fleetwood