I have a C4 (automatic) and I run slicks. My best 60 is a 1.62.
Im sure my technique is alot different than yours. I try to keep my weight down as much as possible so I only run w/ less than 1/4 tank. You didnt say whether youre spinning or not. If you are theres obviously a whole bunch of reasons for that. Not getting the tires hot enough or just simply coming out too hot. Independant rear suspensions are not really suited for drag racing. You obviously want a soft suspension set-up in the front to get weight transfer and a moderate set-up in the rear to get it to squat. You might want to contact some suspension companies for adjustable coil-overs and shocks (if you havnt done that already.)

I havnt run the nittos personally but anyone I know who has uses around 15-18psi w/ a real good burn out. Radial tires dont heat up near as fast as slicks so you have to do a longer burnout. Youll have to be a little more specific w/ your problem (spinning bogging etc). Hope you get it to hook. Its an awsome feeling.