Step-by-step explanation
What is the angle of the driveshaft.
Relative angles are IMPORTANT more important than absolute angles. You say that your trans is 1 degree off of horizontal and the rearend is 4 degrees off of horizontal. If the driveshaft is 2-3 degrees off of horizontal, then both U-joints are working at a 1-2 degree angle and they will cancel each other out, all is well. If you have one U-joint at zero and the other at three, or worse 1 the other way and 6 at the rear, your life will suck.
That reminds me, I really don't like to see U-joint angles of over 4 degrees under any circumstances. Which is why sometimes you need to point the pinion down instead of up, so the U joint angles are complementary even though the absolute angles are screwy.
The key is, you want both U-joints to be working at close to the same angle as each other.