George,
Your photo shows a very clean engine with a few mods -- and a very clean garage with some nice features.
First, what is the engine history - mileage, previous work, maintenance, oil used, etc. ?
If you have 100K + then maybe it is time for a full rebuild - your call.
Options for your consideration:
- leak down test first to check valves and pistons
- oil and filter examination looking for metal particles
Checking the cam chains:
- remove muffler
- open up chain covers
- examine chains, tensioners, guides
- determine if this is the major problem
- if this is the problem - fix and drive
If you have decided already to do a full rebuild then proceed with a full tear down and inspect and measure all parts for wear tolerances. If you have read the threads on this forum then you know this rebuild is expensive - 5K-15K even when DIY.
If you want to get a bit more power then explore cams and chips -- there are several excellent suppliers.
We are in the middle of a 3.6 rebuild and found many parts to replace that were not suspect ahead of time. But, this engine had very little recorded history.
Regards,