I would also buy a pushrod length checker excessive "sewing machine" sound comes from wrong lifter preload and wrong pushrod length. Aftermarket cams have less base circle than stock

 

Make sure to rotate the valve train 3x to different locations when torquing the rocker bolts. When reusing old lifters they still have some oil and residual pressure which can skew the torque readings.
Manual suggests torque, rotate 90 degrees, torque, 90, torque.

 

I was going to say the same thing.

 

No need for the push rod length to be checked, if they are stock he is fine. I am running the same set up and using the stock pushrods. This was verified a few times by my-self, they are fine with the GT2-3. I would suggest pulling the rocker covers off and checking your tq on the rockers.

 

so your saying the gt2-3 has the same base circle as a stock cam?

 

I am saying that the stock push rods are OK per LPE, I even called again today to make sure. I have well over 30K on mine without an issue. I think there is another problem with his truck, just wish I could hear it.

 

I've had this problem a couple of times ... or something similar to it. Definantly check to make sure a bolt didn't back out.

What kind of motor oil do you use?

WHat I'm getting at is it could be a lifter that hasn't primed itself back up. Although, in 400 miles it should have. If it's a very THICK oil, then that could be why. It sounds VERY brutal, but IF that's what it is, the only way I've been able to get them to stop is by cold revving it, not abusively though. I've just revved it enough on a cold start to kick the oil pressure up to 80psi or close to it. It doesn't happen immediatly, but it will eventually.

It could be a bad lifter too like already stated. That's not ot uncommon with bigger cams and stiffer springs.

 

You don't remove the lifters for a cam swap.

The rockers aren't the old stamped steel type. They are 'roller rockers' from the factory.

 

the stock lifters can take up alot of slack around .100 Im sure this is why they are saying this, personnaly I like knowing my geometry is correct even a difference of .02 can make a difference with trips to the track and lots of mileage from daily driving.

 

I had a bit of a problem with mine. Check the pushrods to see if there is any blockage. I would clean them up and make sure no gunk got in there. Make sure you can see straight through them.