pulley install wont fit?

I got a 2003 silverado with the 4.3L. I bought the jet pulleys for my truck and the wont go on. anyone else have this problem?

oh i for got to tell that its the bolt holes arre so close to the edge that they want to go in sideways and cross thread.

Did you confirm that you got the right part?

Try installing one of the old pulleys and see if you can get that to go on. Maybe you just have them a bit off center?

The old pulley fits nice. i checked and it is the right part #. I tried to put it on for like an hour. Then it took only 5 minuits to install the old one.

I figured out the stock bolts wont work on this install. If anyone else is having trouble with this same thing you need to go to you local bolt store and buy 3 3/8" x 24 x 1 1/4" allen bolts. Then the pulley fits with out any problem. Jet Performance also dont tell you but you need to buy a smaller belt. I went with a 930 belt but might need to go up to a 935.

Are these underdrive pulleys? I did a search for underdrive pulleys and could only find ones for a chevy cavallear 2.4L.

Are underdrive pulleys effective for trucks or are they more for racing?