not shifting into overdrive

Tranny is 46rh automatic.......I replaced od/ lock up solenoid inside the tranny , put fresh atf 4 tranny fluid in it along with new filter.......still not shifting into overdrive...I've been driving the truck over 2 years with out overdrive ......I don't drive the truck over 55mph. Because of the no overdrive shift problem........I did the obdi fault code thing by turning the ignition on and off 5 times within 5 seconds.....and code 12 37 32 55 came up......looked at the trouble code chart online........37 means.. Ptu solenoid....or tranny temp sensor.....so I called the local dodge dealer.. the parts guy said not showing anything for a ptu or tranny temp sensor.....and he even asked the tranny mechanic and I still can't get an answer why the tranny won't shift into overdrive....... By the way code 32 is egr problem which I will be replacing egr ......12 is code for 50 starts ..55 is code for end of trouble code............anyway.......I still drive the truck everyday without od........ Now its driving me nuts cause I don't know why its not shifting into od......... Its a work truck and I'll drive her into the ground....I'm not sinking any big bucks on tranny rebuild or replacement........ Hope it is just a simple fix...........please give me an answer!!!!!!!!!!!!!! Going bonkers!!!!!!!! Can't get an answer from anyone....please help!!!!!! Thanks