stock98ws6

I just wanted to introduce myself, and had a couple of questions. My name is David and I have a 98 Ws6. Growing up as a "90s" child i remember seeing these cars on Tv and in various magazines. I vowed to one day own one. I am 21 Years old now and have had almost twenty cars (mostly mustangs) since i turned 16, and this is one of the cars that I am going to keep. It has about 130,000 miles, and some mods. The mods include a built rear end (3.73 gears, moser axles, trickflow rear end girdle), a built transmission (cost me like 3000$, and was built by BradCo), Granatelli lid, and true duals with bullet mufflers. The car runs great except for one problem under wide open throttle it will not shift into the next gear. Driving around town it is perfectly fine. i was thinking because I changed the converter size that I would need to get the PCM reprogrammed, but I dont know. I would like to know y'alls insight on my problem.

I also plan on doing some future mods to the car, and I was wondering what budget friendly mods would help me pick up some et times. I was thinking about deleting the ac, and switching over to a manual rack. The car is mainly going to be used for some racing in Mexico, and the occasional drive to work, which is less than 5 miles.