I think your driveline angles are off. I would read up here and go from there:
Driveline Geometry 101 – Tom Wood's Custom Drive Shafts
Since you mentioned you extended the driveshaft, I have also seen on some builds where the driveshaft was extended too far and the slip yoke was bottoming out on acceleration, giving a feeling like axle wrap. I would double check this. With that much lift, it may come down to needing a double cardan (CV type) shaft.
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2014 Super White Trail Premium My build thread:
http://www.toyota-4runner.org/5th-ge...ld-thread.html
2008 SR5 4X4 V6 Better late than never build thread:
http://www.toyota-4runner.org/4th-ge...ld-thread.html