I am stumped. one of my trucks is an 02 2wd auto 3500 drw. use it for heavy towing of 15k or more. when towing heavy on a couple of mild TX inclines at about 70 it will usually do a hard downshift into 3rd (i think) and stay there until we pullover and come to a stop. then we can start again by manually shifting to nuetral and then back to drive. This truck has a rebuilt trans with the usual heavy duty parts. fyi the fluid is at normal level, somewhat discolored but not filthy, the motor temp is 190 and i put a new thermostat in becasue it was jumping up a bit high. solved that but cannot figure out this downshift. i talked to 3 shops with on answers. seemed to me that they should have had some idea. talked about grounds. cleaned them to better than new. what do yall think i should look at next before i end up having to rebuild again at a suncoast dealer shop? thanks

 

Have you called suncoast about this? Beening that the trans down shifts into 3rd under heavy load that the converter is still locked up seems normal to me.The shifting into 1st or 2nd and it has to done manually is that the Transmission governor pressure solenoid or Transmission governor pressure sensor is bad. Do you have a voltage regulator like a DTT or in line resistor?

 

honestly this could be one of many problems and thats the bad thing about transmissions they are hard to diagnose without seeing them. i would start by pulling the pan to check for and metal pieces other than normal materials from wear. it could be sensors but it would kick in and out of gears and would kick out of 3rd as well. also depends on who built the trans and how many miles are on it. also what clutches and electronics are in it. sun coast has a new style pressure sensor and governer for the 47/48re that are modified from the allison 1000. and if you change the trans just order one straight from suncoast you wont regret it. i beat on mine every time it out on the track 2-3 times a week with no issues. but by pulling the pan it will rule out the mechanical side of issues if nothings floating around. and you can pull the pressure and govener out and check them to see if they are stopped up. a single peice of lint or debris can stop the pressure sensor up. or order the new suncoast governer kit to replace them while down they run 139.00 msrp. well worth the money.