Hey, I am putting on a 4" lift it has adjustable lower control arms. I know a SYE is recommended, But do to lack of funds I want to put that off for at least another year and or two. (I will be having the lift installed by a shop) It will be a daily driver and see moderate trial use occasionally.
My question is: If I also have the adjustable rear upper arms installed will that, combined with the t-case lowering kit, mitigate the effects of the 4" lift? (at least fairly close to that of a SYE kit) I figure going that route I can save about $550 in costs of the install according to the prices several shops in my area have quoted.

Some TJs come from the factory with a vibration in the rear driveline. There's little you can do to make that go away without a CV joint. All the slip yoke eliminator does is lengthen the rear shaft a few inches. That does result in a slightly less severe angle. When your only method of adjustment is the lower arm, the position of the axle may not end up in the best location.

The theory is that as you bring the bottom forward, the nose of the pinion kicks up toward the end of the Transfer case. When you over stress the front motor mounts and lower the skid plate, you also change that angle back toward something more normal. Every jeep is different.

Long ago, as in my CJ days, I went to CV shafts and I've never looked back. If you decide to test your luck, you need to become practiced at joint replacement. Better still, learn how to grease them constantly and replace them frequently. The cost of one tossed rear shaft will probably exceed the cost of doing it right.