xwkid

yeah I agree o2 sensor

sounds like o2 sensor to me , your car should lean out on inital opening of the throttle then o2 sensor corrects your mixture. most o2 sensors and cat convertors wont work as they should untill around 500 degrees , I think the resistace of your o2 sensor is not with in spec at N.O.T that's why you have this problem on the highways.

is it a ba ? if so it may be valve boucing from s*$t valve springs.

oil after the turbo sounds like turbo oil seals from oil seal failure , only other way is if the intake (suction side ) has a restriction and the turbo draws the oil past the seal .

ive just had fitted a hayman reece towbar with the upgraded tow pack inc drawbar arms and a heavy goose neck , I wouldnt go for the under bar type if you intend to tow things over 1000kgs. keep in mine atuos can tow more weight than the manuals. my stock fg turbo manual can tow a car tralior with a xw on it with no problems, on the highway I get approx. 15L /100kms and dont use 6th gear. I got the towbar mob to keep the bit they cut out of my bar in one piece so I could glue it to a blanking plate I got for supa cheap. and looks tidy.

nick the wog has no idea what he is doing I would never go there. use someone else.

as your valve springs become weak your engine will begin to valve bounce ( sounds simiar to the rev limiter working ) popping sound out the intake or out the exhaust pending on which springs are failing. I wouldnt be concerned about your springs untill you start to do mods, eg , change of cams, upping the boost or rasieing the max RPM's. as for price goes they vary in price from $300 for a crap set and up for a good set . when you buy your new springs it is very important to get the right seat presure , installed height and max lift heights when selecting your springs also the valve spring harmonics must right. type in valve spring harmonics on youtube to explane what this is about. hope this helps.