Not good vibrations c12

Hey fellow Truckers..
Got a 07 Shakeliner tipper with a c12 2ks 900k on da clock and eaton autoshift got a vibration/shake its seems more engine vib/shake driveline/tranny i say this because done all king pins tie rods bearings new steers fixed vibrations but its as if i can feel this more because sorted those issues out. happens higher rpm round 1200 to 1500 its much more severe loaded and seems underpowered struggles loaded its doing my head in its not speed related more rpm.. no fault codes fuel pressure good oil pressure too, regualy serviced new filters etc new reman turbo any ideas where to start? Oh n havent had valve n jake adjustment in 100k kms? any other things can explain to help diagnose? Just a young aussie trucker who loves my american truck giving it a crack and sick of mechanics/companys not giving a s#it. Thanks in advance

 

Cheers for reply Jspat67 ive been under there got no up down play on shafts and have greaseless ujoints they all seem ok....and forgot to mention had bearing and yolk from rear of tranny done im thinking it might be my driveline angle it was out so changed the length of the leveling rod on my airliner suspension and now is to spec but after that i got new rear tyres could that affect my angles? Also i do have a bit of oil seapage from the back off the first diff i know it might be obvious but could that be the issue? Also how would i check that driveshafts/yolks in phase? Ill try get it sorted an give an update. Cheers