These early EFI motors are smothered badly, as already pointed out the exhaust is restrictive but the cam is also rediculously small. That wouldn't be too bad but the motor is also wearing heads that were designed for a 289 so all combined it's operating FAR below it's potential. The single best thing you can do to help this motor is change the cam, heads swaps are good but for $229 the Crane 444232 simply outguns all other mods on the bang for you buck scale, combine it with an exhaust system and you'll have a truck that performs the way it should have from the factory. And the best thing is it'll behave just as well as it does not, smooth idle, no codes, just lots more power.