I am curious why you would go from an 87 mm to a 90 mm. That is like changing from one flowing 850 cfm to one flowing 870 cfm. If you are feeling you are not getting all the hp/torque out of your engine Run a good 20-30 minute scan to check the tune and Injector Duty Cycle. The 04 Corvette Z06 made 405 hp with your TB at less than 80% IDC and the T1 Corvettes make 380RWHP with that TB.

 

Like already stated you have a 78mm tb now..To move to a bigger one you will need to go with a 4 bolt intake mani-tbss/nnbs manifold..
For it to work you will need the torqrush adapter so the whole manifold swap will run about $500-600 depending if you buy used or not..

Your not being limited by the 78mm tb on your truck now..Plenty of guys make good power on the stock intake manifold..
IF you still want to do something have the tb ported by S2 Performance (.net).I would consider the 90mm intake mani a last mod to do as the returns vs cost is fairly low