Well, two years since I last ran the car, and I'm having the same problem (only more severe this time). My times were 12.044 and 12.067 on two consecutive passes, and I went to jet-up, and didn't have the right jets for the rear, and couldn't buy any at the track, so I just raised the float level a little bit, and got another .10 out of it with 11.905. I'm still off by about 2-4mph on the top end, and my 1/8 mile times are right for about 11.75-11.80, I'm just dropping off on the top end.
This is the first time I've run the car in less that 98*F air, and the humidity was low (65%) so I thought I could get a PB out of it, but I think I really need more fuel. Of course, I grabbed a box of spark plugs to swap in when I got to the track, but hadn't labeled the box "used," so when I opened them up, I got a nice little surprise. It was impossible to read them, as I've put about 200-300 miles of street time on those plugs.
I also had a bit of a wierd vibration or shake at the top of second gear - it might be time to pull the TH350 and root around in its guts a bit. I really don't want to go back to the TH400 and have to get another driveshaft...
Anyone who's interested can see my combination here.