TH-400 torque converter

[West Coast GTO]

Just sorted out the many issues with my 455 rebuild and ran the car at a local cruise night. Engine ran great but the TH-400 would stumble off idle and shift erratically/ slip during easy throttle. During aggressive throttle, the engine make alot of great noise but not really alot of acceleration.  The Th-400 is a non original 67 unit with a 2200 flash converter in it and no shift kit. I believe it came out of a large model Pontiac because it had the long tail shaft when I bought the car( that has been changed out). I do have a TransGo reprogramming kit for the trans that has not been installed yet.
Should I be looking to install the kit or invest in one of Cliff's 9.5 inch converters?
Engine is a 455 with .30 over, hydraulic can with .490 lift on 112, RPM intake, Edelbrock heads, Brawler 850 carb, Davis HEI and Ram Air 4 exhaust into 2.5 inch pipes. Idles at 800 with 13 inches vacuum and 160 psi compression.

[Cliff Ruggles]

The 9.5" converters are EXCELLENT.  I sell gobs of them and they get raving reviews.  Each one is custom built exactly for the application. They are however expensive, but worth every penny IMHO.  We use them here in everything we build and wouldn't even think about using anything else.  These converters are no bigger than the soup bowl you had your lunch out of, and when you first see one you're thinking there is NO WAY this will ever harness the power of my 455. 

However they drive really nice on the street with excellent torque multiplication yet really "tight" for normal driving where you hardly even know it's in there.  Any full throttle hit and you'd better have your seat belt on and you hat and glasses laying on the passengers seat because you will be holding on for dear life and your hat and glasses will be up in the back window!!!.......