Hello people I am wondering weather to build my 138k mile, 3.1 V6 or do an L98 TPI swap.

I really would love to get alot more power out of my 1990 firebird (700r4). I brought it back to life, ive owned it for 5 years since I was 12 so selling it for another car is out of the question. Now Recently i have been trying to find a parts car and people are just not working around my schedule or difficulty like that. My goal is to have a completely reliable engine that I could drive cross country with if I wanted to. Maby 280-300 horse power if I did an L98 swap but I would be happy around the 180-200 park with my 3.1 if Possible. One main reason I had a swap in mind is because I would get better MPG. My Neighbor has a 91 GTA l98 and gets 19 around town mixed highway and I know he floors it every chance it gets. If I drive like that in my 3.1 I get between 15-17. Best I've gotten is 21 and that's mostly highway going under the speed limit.

I am really in a pickle here and if there are ways to build my 3.1 without Killing my gas mileage. I was thinking of doing a 3.42 posi rear end over the winter but I do not know if those gears will fit in my current rear end or what my friend would charge me. I Have a 2.73 posi unit out of my friends old rear end out of his trans am and could I use the posi unit in another gear ratio? Would a posi rear end like that kill my MPG in my 3.1?

Over the winter I am definitively cutting off my smog pump and catalytic converter and putting a straight pipe where it was, and if I am keeping my 3.1 for a while pace setter headers. I Currently have a cat back dynomax exhaust, slightly larger refurbished fuel injectors and a cold air intake so I know I am only pushing 142 HP AT MOST. I hear 3.4 aluminium heads will work on my block and a cam upgrade from a 3.4 but I am not sure. Are there any performance chips out there that I can plug in and gain any power or MPG off the shelf? I do not know much about tuning chips or anything like that.

I am really considering freshening up my 3.1 with a couple small mods and waiting to find a perfect parts car and eventually doing an L98 swap. I have found whole parts cars in my area cheap with running engines and WS6 suspension and everything I could possibly need. But if I can get 200 Horses out of my original V6 engine I would more than happy to do so without killing my mpg. This is my daily driver excluding winter time and I make minimum wage so I would like a nice hot rod with good gas mileage.

Any info and suggestions would be greatly appreciated thanks guys!