The 4.5L is a pretty good donk in regards to reliability, thirsty bugger that's for sure. I'm pretty happy with my 4.5L auto wagon which also has LPG fitted. A little under powered when going up steep hills but other than that mine fly's on the open highway. Mine has 253000 odd K's on it has been regularly serviced doesn't use any oil or water doesn't blow any smoke and no signs of oil leaks, I have been told these engines are basically bulletproof much like the bigger 4.8L brother. If it ever comes to an engine rebuild I might look at fitting a supercharger or such just for that extra bit of grunt for the hills. I'm not aware of any common problems with the 4.5L at all.
I have a 4.5 that has done just over 300,000Ks - they are tough and reliable but very thirsty. It will cruise all day at 110 but is a slug up hills and the auto, whilst strong, continually shifts up hills. If your budget can stretch to it I would get a 4.8 - much more usable power and no thirstier than a 4.5.
very reliable donk,mine uses20 to 25ltrsgas a 100k=$13. to$15, a 100k that's with muddies, lift ,steelbar and winch , fully loaded with gear,climbs everything in the high country ease.on petrol it uses 14 to 19ltrs a 100k =$18 to$25 to a 100k
Good news bigfella, i got mine at 70,000 and had a few overheating probs but new rad and viscous hub sorted that out, have changed auto oil twice and had to get tappets adjusted once. Auto oil is clean as and engine oil is pretty clean every 10,000 service. I have no oil leaks anywhere it is like new. I love it! But it is a bit of a slug with 2 ton caravan on the back.