I used hp tuners on my trans am. There are tune archives and most times you can find a similar tune to what you need. Of course it would still need fine tuned, but usually close enough. You don't buy the tunes, but you purchase credits for each car to unlock the software to be able to tune. A tuner would buy the credits in bulk. Only issue is, you have to go back to the same tuner or you'd need more credits for another tuner.
68 Road Runner, 69 Belvedere, 71 Challenger Vert
340 barracuda, 01 Ram CTD, 95 Ram, 04 Ram, 85 Daytona turbo Z
99 Trans Am, 66 GTO, 06 Magnum RT AWD