Power Loss--Need Help

[DangaCustom/10]

Hi all,
I have a 1972 Custom/10 Deluxe that I had just finished restoring. It has a 375 hp and 400 ftlbs torque 355 small block backed by a 1993 700r4/4l60 overdrive transmission with a 2200 stall converter. It has a single piece driveshaft and a auburn gear posi unit with 4.10 Richmond gears in the rear end. I was thinking I was putting together something, which in theory, should be relatively fun to drive, however, after I hit 2nd, 3rd, and 4th, there is a huge power loss. if feels as if there is no guts or power being put to the ground in low rpm. I can step on it and it won't do much. I did fix a problem with my fuel pressure, which did help a little bit but now I'm at a loss for ideas. Truck cruises nicely at 115km/h at 3000~rpm on the highway which is nice but it take a while to get there.

We have noticed that the distributor "pings" and the carb needs to be rebuilt. I'm thinking timing will be a big factor but I feel I went the wrong path with my rear end gears and transmission.

Any ideas??? Any help is greatly appreciated.