Strange vibration

[Sil80315]

Im getting some unusual vibration that im feeling in my peddles and the floor.. It doesnt seem to happen all the time but mainly after a few minutes of driving I start getting a thumping vibration when i start pressing on the gas. Ive pulled over and reved it a few times and it has this little thumpin im feeling and im thinking its gotta be like the flywheel or clutch cause I dont feel it in the shifter but mainly through my peddles

At first I thought it was from the new rebuild but I couldnt see that being the problem seeing it only happens after awhile of driving and its really not a noise its more of a feeling.

Anyone have any idea what this could be? Either way im dropping the trans tomorrow and checking it out