If your Comp G is an '04-'05 then you have nothing to worry about for a mail order PCM from DHP. They have been tried and true for years and work great. As long as you have some form of Headers/180* T-Stat/Colder Plugs/3.6" Pulley/Intake...then you'll be fine.

If not, you can buy a used DHP Powertuner or a new HP Tuners suite.