How do I determine if I need Pinion Shims

[Arl37]

I have a 69 C10 Fleetside. I put 2 1/2 dropped spindles on the front and 4 Inch dropped leaves on the rear. Both from Performance Online/Western Chassis. The truck also has 1" dropped shackles in the rear. So it has a theoretical 5 " drop. Had tires rotated and balanced today and the front end aligned.
I " think" I have a minor vibration or throb when I floor board the gas pedal. I don't think had this before I lowered the rear.
The truck also has a two piece drive shaft. The Carrier bearing carriage has one hole remaining at the top so i could move the carrier nearing up one hole. The person who aligned it said I should move the carrier bearing up.
The pinion end of gear case has a decided downward tilt. Don't think it was like this before. A service tec at Western Chassis said dropped trucks should have the pinion tilted downward.
Need less to say I am a little confused.
Can someone tell me how to determine if I need Pinion shims.

Thanks

Ed