what has been done to the motor is it blown, how about the intake system . i am a lighting owner and dont know much about saleen packages. i have several mods on my truch which is an 02 model my last trip to the dyno tuner i use my truck was putting out 422hp at the rear wheels.i can list the mods i have done if that will help.
Yes, it can be removed by any competent SCT tuner. You can't use an off-the-shelf tuner on the Saleen, you have to go with custom tuning. You can pick up some power but Saleen's setup has a habit of pegging the MAF so that needs to be addressed if you go with more boost. The same MAF on a Roush intake has no problems even with 3 lbs more boost.
if you want more power you need to get an sct unit. however do not use a store bought tune. there are clubs in all areas of the country find the club in your area they will help you find a dyna-tuner in your area who is good with fords and have them tune your truck. dont forget every mod you put on your truck will have an effect on your tune. do the big mods then dyna-tune. i hate to be so worde'y but when you start putting mods on your truck you dont want to blow it up. hope this info helps.