Like olddog already suggested, your current EFI if speed density based, will require adjustments for any atmospheric changes to maintain its tune. If you have a speed density based system that can also supports a Mass Air Flow (MAF) fueling model you would be much better off with the MAF based fueling model. The MAF based fueling model automatically adjusts to changing ambient air conditions. From Denver to Death Valley you don't have to do anything but drive the car.
If you decide to go to the MAF based fueling model you will need to get a MAF sensor. If your engine is basically stock you can use one of Ford's sensors for your style engine. Otherwise you need to go aftermarket.
If you go aftermarket the best sensor choices come from Pro-M Racing. Pro-M was started by a Ford calibration engineer that was involved in Ford's original decision and deployment of mass air based systems. Each Pro-M sensor is flowed at Pro-M and provided with a MAF map for your tuner. The signals are cleaner by an order of magnitude than other commercial alternatives.
When most of the current aftermarket suppliers of MAFs began offering products the firm that did the MAF calibration for them was Pro-M. The Pro-M MAF you would want for your application is this one =>
Pro-M 80.
If your current EFI does not support a MAF based fueling model and you want to go there, the Pro-M guys also sell model specific and universal
self learning EFI systems based on a Ford factory racing ECU, click here =>
Pro-M EFI Universal Hot Rod System.
There is a fairly good used market for FAST systems. If your FAST system does not support MAF based fueling and you want to go there, you can sell your existing FAST system put the money towards your MAF based system and reduce the cost of conversion.
Ed