Strange vibration, no luck on source, need help

About three weeks ago I replaced my stock headers, stock H-pipe and dynomax catback with BBK 1 5/8 unequal shorties, BBK H-pipe with cats and Flowmaster Catback (all 2.5").

The engine is basically stock except a BBK CAI and 9mm plug wires. AOD transmission.

I had to shimmy the driver side motor mount with 3 washers to raise it off the steering arm. I switched to locking bolts on the headers to keep them from backing out (they backed out once and fried the gaskets).

I am feeling a strange vibration around 2300 / 2500 RPMs. I have taken it to two mechanics and two muffler shops. They cannot find anything wrong with it and tell me everything is tight, nothing is rubbing up against anything else.

I had the muffler shop cut the hangers from the transmission today to see if that would fix it, nothing.

My last idea is to have the motor mounts replaced (could that be the probelm)?

Any ideas on anything else I can check or what this could be. It did not do this under the old setup.

DeadLifter said:

Wouldn't hurt to double check again to see if mufflers or tail pipes aren't rubbing against the frame anywhere and that you shimmed the motor mount enough. I've had problems like this after installing exhaust with the headers on steering arm and tail pipes rubbing frame.

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Muffler shop checked the exhaust twice, it is not touching or rubbing anywhere. There is about 1/8 to 1/4 of an inch between the header and the steering shaft. No vibration in the steering wheel at all. The mechanic today said it didn't feel like it was the exhaust pipes themselves and he felt it anytime the throttle was pressed hard. To me it feels like it is coming from / near the transmission, the shifter and floor pan around the console vibrate. I just drove it for the first time today and it vibrates even when I take off slow.