If it was my car I'd put a SFT cam in there somewhere along the lines of a Mopar 0.528. I don't think I'd actually buy a Mopar cam anymore since they are super expensive and the the QC is spotty but just something in that range. With 4.88 gears you might want even more cam than the 528 but it is only 383 cubes and you mentioned that you wanted some bottom end torque. Actually I'm having a hard time figuring out your combination since you have a dual plane intake and 4.88 gears. Those two things usually don't work well with each other but I suppose the 33 inch tire kind of mellows out the steep gears.

I'm not positive what the issue is with your combo but it could very well be that the hyd lifters are heading home just when the rest of the combination is getting ready to party. All it takes is one part in the engine to quit early and the whole combo slows down. Of course you could also have some other issue such as fuel delivery, ignition, etc. Lots of things can kill the power.