Help with driveline alignment!!!

We do entrance road racing with our 1995 S10.

I have a Richmond Super T10 transmission and Explorer 8.8 rearend. As you may know, the differential isn't centered in the rearend. It is offset to the passenger side. We have a custom driveshaft made by a local shop and had the balance rechecked - it was fine.

We've had a mad vibration at 4,000 RPM that may be due to a failed tail shaft housing (we recently replaced it) but I suspect we have some driveline issues.

Our transmission points 3 degrees down towards the rearend. Our pinion flange points up 3 degrees towards the transmission. Of course under load the rear axle will twist and that angle will increase.

This doesn't seem correct to me.

Any help appreciated.

axle pinion being offset doesn't really change much
make sure you have plenty of plunge left on the slip yoke
assuming you have a reg cab with a 1 pc driveshaft, 3 down on the trans, 3 up on the pinion would be the ideal angle under max load. typically you would want the pinion to point down a touch more (amount based on how much wrap you get.
try tipping the pinion down a degree or so if you think it's a driveline angle issue. so make it 2 degrees up instead of 3.
4k rpm at what? the engine rpm or driveshaft rpm?
if engine, in all gears? anything happen before 4k rpm?

The yoke is inset according to the specs we read on Richmond's site.

4,000 rpm on the engine. We don't have a tach on the drive shaft. 

We only notice it in 4th gear, but they may not be the only gear. We whiz through 4,000 RPM so fast in the other gears it may be a little tougher to tell in them. I could do a test drive (when we get the truck back together) and do a purposefully slow RPM climb to check them as well.

My gut says the vibration was due to the (90% around the circumference) crack in the tail shaft housing.

just to make sure might as well check to make sure you have at least a minimum of 1/2" of plunge from ride height. (that's an out of the ass number, but any less I'm pretty sure you'll bottom it out)
a tailshaft housing wobbling will definitely make the slip yoke wobble causing issues, but I feel like you would notice it in more than just 4th gear.
hopefully it fixes it though!

Thanks.

We'll find out in a couple of weeks once we get our new dash, race gauges, and Lithium battery installed.