Got this car about 8 months ago. It started leaking transmission fluid and slipping in 5th gear after about 4 or 5 months. Bought used tranny and had a transmission shop replace it. The new onewas doing the exact same thing. Got a claim on the tranny and they sent another, 3rd tranny doing the exact same thing. Starting to think it's not the transmission. They scanned it and i scanned it and there are no codes. This has a z1 intake and exhaust and is flame tuned. HELP.

Makes me think you have a bad TCM, is your TCM located in the passenger footwell below the glove box?

If so that's your likely culprit. 2003-2004.5 had an external TCM, 2004.5+ the TCM was inside the transmission.