Vibration under hard acceleration

[ghabe]

I installed Doug Thorley long tube headers and y-pipe last week on my 2004 V8 4Runner. Since then, I can hear and feel a strong vibration under hard acceleration. It's not present when accelerating slowly or just cruising at a constant speed. This vibration definitely wasn't there prior to installing the headers. I immediately noticed it the first time I accelerated after the install.

I'm thinking it might be the motor mounts since I had too loosened them to tilt the engine when installing the headers. However, at first glance, I don't see anything unusual. Any other suggestions before I pull them out? The driveshaft is tight.

 

[ghabe]

Upon further investigation, the issue is caused by the front driveshaft hitting the DT y-pipe due to insufficient clearance. More specifically, it's one of the zerk fittings that was touching the y-pipe at higher RPM. The temporary solution was to replace the zerk fitting by a bolt with a lower profile. I'll but the zerk fitting back when the driveshaft needs to be greased.

Since the issue was only occurring at higher RPM, I'm assuming there is some play in the front driveshaft and it moves more as it spins faster. Could this be a sign of worn u-joints?

I didn't have any issue prior to replacing the stock y-pipe. Clearance with the DT y-pipe is really tight.