I can't find anything on here with this exact issue so I hope this isn't a repeat. I'm having an issue with a 2008 WRX Auto w/ 36K miles.

Here are the relevant mods:
SPT Catback Exhaust (other exhaust parts all stock)
Pro Dyno/road tune
Cobb AccessPort

I haven't modified anything in about 2 years. Just recently, in the last 2 months, I have had some random slow starts and dropping idle speeds. When I first start the car after sitting a day or many hours it starts fine. If I drive it and then start it again in less than 3-5 hours is takes about 4-5 cranks rather than the usual 1/2 crank to start. Also...when I come to a stop...the idle will randomly drop VERY low and shake the car like it wants to stall. If I put it in N...it's fine.

I have replaced the CAI filter, fuel filter, and battery. This didn't help. I also had the recommended 30K mile service about 4 months ago and had all tasks completed as listed from Subaru. I also am not getting any check lights or codes using the Cobb diagnositc in OBD port. Are we talking fuel pump or O2 sensors...or some other sensor? I can't imagine ANYTHING going bad with only 36K miles, but hey...what do I know??
Of course...it's out of warranty now and dealers charge an arm & leg just to diagnose.

Any help/opinions would be appreciated...thanks!