Wassup i just bought some 20" rims today and itz some intense shakin over 40mph but the lug nuts are tight i was wondering what else could cause it

was the shake there before the rims went on???

Are the rims direct fit or do they have elongated holes that need to be properly liked up and torqued supertight to hold in place?

i hope they were a 5x115 bolt pattern

Why? GAMEOVER ran 5x114.3 20" rims..
Were the tires balanced?

sounds like they weren't balanced correctly. do the 5x114.3mm wheels really have a hard time fitting? I have been looking at a set of rims that is listed to fit the bonneville but has that pattern. has anybody here had problems with vibrations running a wheel that has that pattern?

running a 5x114.3 is not recommended

No. Thats what mine are
Just make sure you torque your lugs evenly in a star pattern. (Not that you wouldn't do that anyway)

i'd suggest having it aligned...when i went from 15'* to 17'* my car rode like crap until i had it aligned...and as mentioned above you may need Hub-Centric rings,they made about a 15% difference for me

Do you know if they put Hub Centric Rings on the wheels before they mounted them on your car? If not this might cause vibration if the rims are not hub centric.