2010 GT500 pulley mod problems

Hello Shelby owners:

I had a recent pulley (2.6 inch) change, idler, and SCT tune from a local speed shop. The engine tuner who installed mods and “custom” tuned the SCT on his dyno and tweaked somewhat is a well known tuner in Pa. He and his partner have been sought after by NASCAR Racing. His partner accepted but sold business to my mechanic/engine mod guy who only does word-of-mouth work (no advertizing).

But here’s my problem or in need of some further explanation:

I had a 2.6 pulley w/tensioner, sparks and SCT custom tune at local speed shop for my 2010 GT Shelby. Am not too happy w/ dyno results. Base w/o mods showed respectable 472 RWHP before, and 502 after modifications. I run 93 (!?!??!) octane from Walmart to keep cost down. Perhaps this is the problem. The performance on the road however sure seems much greater than the 30 RWHP gain even with Walmart premium gas. The custom tune by the shop's owner is somewhat confused too. What gives? He thinks I need a larger throttle body (stock is dual 60 mm; he wants 65 mm or greater). I realize more air means more fuel means more power. Pundits on this forum feel that the TB and CAI are not limiting with the 2010 changes Ford's SVT made to this system. He also feels that I need a higher performance CAI w/o resonator (perhaps restricting- resonator delete) and a larger intercooler. NOBODY else recommends this at this level of change, ie smaller pulley. Maybe I need an alternate tune say from Evo or VMP. I, however, since switched to Shell's 93 (POST-DYNO) and the performance is awesome. Please post comments.

Any help from current problem will be surely appreciated!!!

Finally would another tune purchased/downloaded from someone recommended here extract the expected performance. I read w/interest that some downloaded tunes are within +/- 2% of optimum w/o the dyno. Thanks.

Minnesotalee