Congratulations on your Ute.
I have done NOTHING to my transmission (not even change the torque converter, which I probably should) and I did great times at the track. I haven't been active at the track for years now so I haven't been up on all the racing stuff but I don't think your transmission is the weak spot. Sure, going with less gears would help some but before you do that, why don't you change the differential? I put a Camaro 3.27 in that helped. Beef up the motor also will make better times.