IMO start with tranny mods, do the final drive mod, tranny cooler, shift kit, higher stall Torque convertor. then worry about engine mods.
IMO you will get much better performance for 1/2 the price starting with tranny mods.

and IMO headers suck without cams..
oh and go back to the stock TB.

tranny mods if you do them all should shave off close to a second off your time.

1998 dodge avenger 4 cyl AT
Mods are:
Not enough