I changed the pulley yesterday from a 3.25 to a 3.1. Anything below 4500 rpm's, I have about 8.5 psi. However, when the rpm's climb past 4500 rpm, boost drops to 7 psi and doesnt move back to 8.5 psi until the truck shifts into the next gear.

Is that normal?

 

Belt slip?

 

Mine did the same thing on the dyno. Since my piece of crap Cobalt A/M guage doesnt work Im not sure what its doin on the street but sometimes it feels like its slipping or losing boost.

3.70 pulley and tight belt

 

Look around the serpentine belt system and around the pulleys to see if there is any black dust from the belt. When I tried a smaller pulley with my whipple it was slippng like hell and there was good amount of belt dust everywhere.

 

I checked for belt dust, and there was none. The belt is tight. Im starting to think that it is the crankl pulley. Going to check it out when i get home. I bought the pin kit from magnacharger, I may have to install it now.