4runner Acceleration Weak

[874RunnerDriver]

Why is it that my 4Runner seems to accelerate better with the throttle only just barely open beyond the current speed? I would think, with EFI, that I should be able to slam my foot to the floor and the ECM would then find the optimum fuel/air mix for the best acceleration. Instead, I have to constantly keep advancing the throttle to stay just ahead of the truck to get the best delta-V, as we used to say when I was flying.

It's a 1987 4Runner, if you hadn't guessed, I recently put a new head on, the timing is set at 5 degress BTDC as specified in the shop manual, the valves are all set per the shop manual, I always run 92 octane fuel, the TPI is still at the factory setting...

Any help or advice would be greatly appreciated!