Xenon,
If you do the math on your tire size you will find that you are not truly running a 3.73 gear ratio, If you go to a tire/gear calculator program on the net, you will find your final drive ratio. If you add a overdrive trans, which reduces the final drive approx 30% your driving rpm is actually lugging the engine. That is why you do not have throttle response, acceleration, and the result fuel economy.
The 3705 Edelbrock manifold is for TBI heads. It will not fit your 454 throttle body. The throttle plate size is for the 1 11/16" throttle blades. The manifold will have to me machined, to accept the 454 w/o an adapter, the machine of this is fairly expensive, because beside machining, tig welding is also involved for the water ports in the plenum area. This mod is not for the faint at heart or wallet. If you have the standard bolt pattern heads/non tbi heads, you can modify the center bolt holes to accept the older bolt pattern. If you are using a non high velocity head on a TBI (the old carb heads) you will not be able to get the throttle response needed to move 6500# efficiently. I have used a 170cc twisted wedge on a tbi and worked very well. I have also ported 093 tbi heads and worked very well also. Dart 180 cc iron eagles work well.
The 700R4 wasn't designed to haul 6500# from a dead start. GM thought the same as you are in the 80's in their 4wd's. The tranny just would not hold up. Too much heat, even with auxiliary coolers. 2nd gear usually goes out first, and with that OD.
I don't know what heads you have, however if you are using 454 injectors you are correct fuel isn't a troubled area, in fact it has too much fuel. Have you watched the map sensor on a scanner, and the O2 readings. How many crosscounts do you have?
Hope I have given you info to investigate
Street Perf
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