First time posting. Been doing lots of reading and research but I'm dreading the worse outcome with my motor. Any help would be appreciated in advance. Sorry about the length of the post.
Vehicle has 160km(100k miles) Originally a US vehicle imported into Canada.
Symptoms: Engine runs poorly and bucks under acceleration. At certain times I can get it to somewhat get up to speed but not without running like crap. Intermittently has a "marbles in a tin can sound" at idle. Most often sounds excruciatingly painful on a cold start. Starts nice when it's ran and warmed up. Has a misfire code on each cylinder as well as a P2293 Fuel Pressure Regulator 2 Performance as well as a P0087-Fuel rail/system pressure too low.

Vehicle had same symptoms and all of the codes as it does now before replacing the high pressure fuel pump(pt #’s-03H-127-025/HPP0012 Hitachi) and new cam follower(03H-127-307-A-VAG). Vehicle ran normal after replacing with brand new hpfp and follower. Didn't drive more than 30 km until it started running poorly again. BOSCH high pressure fuel sensor(G247/0261545059/06J-906-051-C) was replaced and the low pressure fuel sensor(G410/03C-906-051-A) on the hpfp was replaced new as well at time of replacing new hpfp. Hpfp is supposed to produce between 507 and 1450 psi from what I've read.
I put a used hpfp on to prove if the BRAND NEW hpfp didn't go bad right away. Same symptoms although almost each time you start it up the pressure in the high pressure fuel line behaves differently each time you start it up and run it. Sometimes 500 psi or less. Sometimes 1800-1850 constantly. Once it ran fine fluctuating btw the 500-1450. This now happens with the brand new hpfp back on as well.
My suspicion is that the timed hpfp sprocket jumps out of time due to a stretched chain, broken guide or failed tensioner. I'm not a mechanic and just my guess.
The marbles in a tin can sound began when first hpfp failed and still continues now. Sound continued after replacing hpfp when it ran fine. This sound is sometimes intermittent usually at idle.
Performed a flow test of the low pressure fuel pump located under passenger back seat and it tested 800-900ml in 15 seconds which is supposedly what it’s supposed to be putting out. Pressure holds when vehicle is turned off. High pressure line holds pressure as well when vehicle is turned off.
Recall was performed by Audi Richfield in Minneapolis of the Fuel filter flange and filter located under driver side rear seat. Vehicle drove back to where I live approx 600km home just fine. This was before the hpfp being replaced. Developed an intermittent fuel odour in the cabin after this service. No odour from the area where the fuel filter and flange was replaced...bone dry!
Before recall and hpfp failure the PCV valve diaphragm membrane was changed along with valve cover gasket. Fresh oil and filter was changed after replacing hpfp.
Spark plugs and coils have less than 10k. Just changed all the coil connectors too.
Attached is a picture of the eccentric fuel pump sprocket with the cam follower removed.
fuel pump sprocket lobe.jpg

As you can see it has some pitting. Sorry about the pic size, not sure how to make it smaller. I thought it was worn down so far that it wasn't pushing on the hpfp plunger enough to produce the high pressure fuel it needs but sometimes I get 1800psi.
Also attached are pictures of my old and new cam followers. Oddly the old cam follower appears to be good despite all the pitting on the sprocket inside.
Cam followers.jpg

I've only had a snap-on code reader on the vehicle. It's going to a local VW dealer to be diagnosed with an Audi scanner so I'm told. Hopefully they could shed some light to confirm my suspicions but thought I'd share this post on here. Being an 07 with this mileage doesn't have a lot of value but the rest of the vehicle is in such good shape and drives like anything I've ever driven. 20 hrs book time to change the chains/guides/tensioner which is going to get expensive if that's what it ends up being or also considering a used motor. Any feedback is appreciated. Cheers