our 4t60e tranny can barely handle the power our stock engines produce and the 4t65e can hardly handle a modified L67 SC 3800. Intense just came out with an amazing performance transmission for our cars and the grand prixes. ZZPerformance is also making an aftermarket sc kit for the NA 3800'*. If you go to http://www.clubgp.com/forum/
you can find the section on l36 engines. There you will find info by a guy named Zooomer. From what i've heard the kit is amazing and bolts right onto our stock engine, with no computer work needed. I've seen numbers around 75-100hp gained, with different sized pullies. I think this would be your best option, however, I plan to swap to the L67 and use the M112 SC.
here are some pages to look at