88 Deville 4.1 hurt :(

Well.....here goes nothin. Speedo just stopped working, spits and sputters on idle and in gear,smoother when driven (coil?).Shifts hard up into 1st and down into 1st,other gears are smooth.digital readout (fuel,heater) works when wants to.Any suggestions? I'm about to install C4 to see if that will help :)

replaced computer :D