How many miles on the new/replacement transmission? Since the speedometer is electronically-controlled, the problem with it is definitely electrical. Make sure the connectors on the back of the dashboard are firmly seated. Do the "wiggle test". Get a multimeter, set it to read resistance and wiggle the wires and connectors while watching the meter closely. You should see no fluctuation in the readings.
The slipping problem could be quite a few different things. Check the fluid for color and smell. If it is brownish or smells burnt, get it flushed. If you have an Aamco near you, they do free diagnostics on transmissions.
Tuesday, April 5th, 2011 AT 10:05 PM