Rattling like a maraca is not a good sign. You say perch collars were installed which requires the coil over to be removed from the truck...was the axle removed from the knuckle during this process? If not, the CV probably got over extended and came un-done.
Rocking back n forth has it's place so long as it is performed gently...slamming between forward and reverse while spinning tires and turning the front wheels too & fro is asking for trouble IMO.
The standard OEM tailgate/hinges are rated for 133lbs. The brace type reinforcements that utilize the OEM hinges will make the tailgate more rigid however they do not increase the weight capacity. Others utilize a Raptor style hinge which does increase the capacity but I forget the number. Maybe...
Have you tried watching the MPG gauge? I don't pay much attention to it but it'll give you a good idea what driving style works for best MPG. Stay out of boost when possible for best results.
Obviously not enough downward pressure on the skinny pedal! No worry, give it another few hundred miles and it'll drop. You'll need to hand calculate for a true number.
If you have the 2.3 there is a plastic drain channel mounted under the oil filter to direct the oil away from the steering components and axle. This will drip residual oil for a day or two. Otherwise I don't understand why there would be oil underneath unless they had a spill when re-filling.
I forgot to mention the knuckles. The kit looks pretty complete, just hard to tell the quality in the picture. 7" of lift is ALOT! I'd be concerned that the everyday ride/handling will suffer. Post up pics if you pull the trigger.
No experience with Belltech but you don't need to go up 4" to run 37s...2" above sasquatch will do it. I'm a firm believer in keeping the center of gravity as low as possible.
Not sure what's included w/ the Belltech kit but if you're going up 4" I would hope it included new UCAs, diff. drop...
That certainly is pretty low price but based on some of the comments the truck started life as a dealer mannequin/demo which would make me hesitant especially being a manual. Demos aren't known to be babied.