I have a 98 Chevy Z71 4L60E and there is no 1st gear or OD after it heats up. I can manuallly shift thru the gears. When cold all gears are there, or after the truck has been turned off gears will shift for a couple of minutes. The diagnostic tool says "Shift Solenoid". How many are there, 2 or 4, and which one do I need, or should all be replaced? There was no code number that came up, just the words. Do I have to drop the pan, filter and valve body to get to the solenoids, where are they? Transmission service, flush, drain, new filter has already been done. THANKS!