The main reason your tranny is going south a lot is because sand pulls tranny really hard and when going slow it causes it to ride the stall a lot and when you are on converter stall you are making heat big time. 5.13's will get you off stall sooner and reduce required average torque load on tranny which means less heat. As  rule of thumb, when you are pulling hard and steady you want to be at 2500 RPM and above as you will be fully clear of stall and making less heat. ANd as you stated you need to go back to a engine driven fan with some serious cooling (maybe even a flex fan) YOur headers are not helping thing because they dump/radiate a LOT of heat in engine compartment and some of that heat is absorbed by tranny through convection. Restoring a high positive air flow will lower under hood temps and engine and tranny temps. You want a fan that kind sounds like a small wind tunnel at lower speed when you are pulling hard. (if you cannot hear it in cab it is not moving enough air) Your usage is kinda severe duty and you need some severe duty cooling too.  

thanks guys yall helped illgive all these things a shot.  its good to talk to some one knowledgable that is not trying to talk over your head.  put a tranny fan and its working better next is the gears unless i can blow the tranny and trust me im trying. ha  

lol  

that sand must be deep and loose,try a small cooling fan attached to a manual switch on your tranny cooler, round here when its windy the sand dries and gets deep,we go to four low and keep the speed up,but then you know that already.sounds like the tires are digging in and pushing sand and not riding over,are those 15.50s aird down enough,probably,well good wheelin to ya