Sticking Throttle - HELP

Deerisftw

I'm not sure if I'm posting this in the right place but here it goes.

I bought my 370 roadster new in march and I've hardly opened it up since. But recently I've noticed a possibly fatal and heavily irritating problem. When I let off of the throttle and clutch in (Or just let off the throttle at all) it has about a half second or a second of lag and the rpm's jump. The jump seems to be relative to how hard the throttle was down. I.e. 10% throttle and letting off gives me about a half second 100rpm jump, and 100% would give me about 900 to 1000rpm jump.

At first I blamed my footwork. Based off of the sound the car was making I deduced that I wasn't letting off of the gas while clutched in, so I began disciplining my right foot by pulling my foot as far away from the gas and granny shifting. Same lag.

Today I took it to my nissan dealership and explained the 'problem' in full and even recreated it for a technician. The man didn't really say much at all while in the car, but later agreed with me, that it was a sticky throttle. They've had my car all day now and about 10 minutes ago they called to tell me that the car had absolutely nothing wrong with it. They even drove it, they say.

Am I doing something wrong? Is this normal? Anyone have similar experiences? What do I do? Is this doing damage to my clutch (smells like clutch)? Etc.

I'll try and post a video to explain further when I get my car back.

OH and other people who have driven my car get the same lag/ theres nothing wrong with my shifting in other people's cars/ and I can tell theres something wrong with it when someone else is driving it because of the sound.