3rd gear lockup issues

[ctd2001]

I have an 01 with a DTT tranny. The problem i am having is the converter locking up in third gear. It seems to have a mind of its own when it comes to locking up in 3rd with the overdrive turned off. Sometime it will lockup like it should and other times it wont lock up at all or lockup around 2k rpms. If i am giving the truck moderate to heavy throttle, it will lock up sooner, then later, but if i am easy on the throttle it wont lockup till 2k+ rpms and around 50mph and i have to easy my foot off the throttle to get it to lock. Once i have the converter locked, if i just slightly lift my foot off the throttle it will unlock. Lockup in overdrive is normal and every other functioning aspect of the tranny is normal, just cant figure out the 3rd gear lockup senerio. I will also mention that last week the throttle was very sensitive and the smallest movement of the throttle made the truck come to life as if i was applying more pedal then what i really was. I did a APPS reset and and ecm reset and the sensitve throttle has gone away, now i just have a lockup issues in 3rd gear. Everything i have read and gathered has pointed me to a bad APPS and i am not 100% sure about this. If anyone has had a similar issue or has any ideas, i would like to hear them, thanks