Car misses, rough idle, seems smooth after 50mph but no power. Noisy lifters or rockers, Oil pressure erratic (10-30-20 back to 30 etc, idles between 20-30psi) Any ideas? High mileage car (335 K) that has been well maintained. I only paid $2000 for it but I hate to spend another $1000-2000 on valve train work just to have bottom end failure. Timing chain and 2 valves was replaced about 5 years ago.(100K) (Double row etc) How about the bottom end on the 3.8? Is it fairly dependable? Is it worth fixing at all?
Any help would be greatly appreciated.

Erratic oil pressure almost certainly caused by faulty pressure sender (or corroded connection where the wire plugs on it)

Were valves changed because they got bent when chain failed? If so , maybe others were bent but not replaced. Compression test will show leaking ones.