I've got my pump turned up one and a half flats. It makes a little difference, but not a whole lot. I have no pyro, so I NEVER run the truck on the highways where it has teh chance to burn holes in the pistons. I stick to city streets, and back roads where the limit is about 60 - 70 km/h. Until I have a pyro, I am not going to chance it.
A PSD exhaust is going to be a good upgrade. It's larger pipe and IIRC it's factory stainless. It's not free but you can find one cheap on a smashed truck or from someone doing an upgrade.
Get the truck timed right, by someone who knows what they are doing...it's not free but makes a difference.
Free in this day and age is a hard thing to come by, but cheap isn't. If you have the tools, then a lot of this work can be done at home if you know what you are doing.