I have found one reason for the torque converter not locking up. On My 2001 Ram 1500, the boost valve retainer had broken and I found the well worn boost valve and spring inside the filter. I found a used valve body and scavenged the spring and pristine boost valve from it. For the retainer, I found a speed shop here in Ontario who ordered a stronger retainer as well as a billet aluminum accumulator (the original made from plastic prone to breaking), 3-4 spring (also prone to breaking and destroying clutches), heavy duty band strut (mine was bent), and a redesigned manual valve that allows fluid to circulate in park, all from Sonnax. While the trans pan was off I also adjusted the bands. The time of the season prevented me from doing a couple of other things while elbow deep in there. Now, the truck shifts are both firmer and quicker!
Sorry for the long read, just an informational post!
BTW, I also had a couple of EVAP codes that were created by a hole in the filler neck where an EVAP tube connects to it.