Engine problems need guidance

[fatman]

Hi guys first time poster long time lurker, and i have a problem with my vzsv6 manual.
Long story short on a trip from Melbourne to Sydney i was heading up a hill all of a sudden it was down on power and running rough no unusual noises when it happened, anyway it made it the rest of the way and back.
So i get back change plugs and coils a few vacumm hoses and it seemed to fix it for all of 30 seconds, next step was a compression test 5 showed normal compression and one had hardly any, also since i have had it it has used a fair bit of oil normal according to holden and now its approx 1lt per 1-1500k and its not dropping any or blowing smoke also no codes ar being thrown, also it runs a bit rougher when the aircon is on.
So any ideas on the cause? If its valves is it worth getting iy worked on or just drop a fresh engine it it?

 

[Nfsve]

1 litre per 1500 k's is not normal for oil use. Most likely Rings / Bore can cause Oil useage and Low Compression.... for the top end you need really worn guides to use that much oil plus valves / seats burnt to loose the compression.
To find out put that piston at tdc and apply compressed air to spark plug hole. Air will either come out dipstick tube/ oil filler cap (remove one) or throttle body (hold it open and remove zip tube - inlet valve), or exhaust (exhaust valve).