318 mystery problem, somewhat solved!

So some of you know that I've had a mysterious problem of getting crazy low fuel economy, 11 mpg highway last time I measured it and I've somewhat solved it by re-timing the engine and re-tuning the EFI system.
But I've inherited another problem. When I re-timed the engine it pulled well but now that I've re-tuned the EFI system, the go pedal just makes everything louder but not allot happens.
The engine's not bogging down or delay when you hit the pedal and power comes on, there just isn't any power there. Any ideas on how I can solve this or is this just how powerful a basically stock 318 is, as I've never had this thing running properly so I wouldn't exactly know :cheers: