I would not recommend engine cleaners - won't touch them personally.
If you've got some extra cash and want to try what worked for me, go to Wal-mart and get the Rotella synthetic 5w-40, cheaper in the 1 gallon jug ($13.??) but you'll have to get 2 gallons unless they have individual quarts.
Then get yourself a good filter, i.e. Puralator Premium, Motorcraft, Napa, Wix, etc - but I don't recommend Fram (not good quality), nor do I recommend Mobil 1 or Puralator ONE (too restrictive and makes some Isuzu's really tick.)
I use to recommend the Isuzu OEM filter, but I don't think it's as good at filtering as I once thought it was.
Run the Rotella synthetic (it IS a diesel/gasoline engine oil) for roughly 2,500-3K miles TOPS, then before you change it, get your engine good and warm, dump it, and start over with more Rotella.
The 2nd round, if your ticking is sounding better, go to 3k miles, and each time lengthen it out a slight tad, as long as things are improving, but I don't recommend going over 4-5k tops at all. These engines crave for very clean oil.
The Rotella is labeled as a synthetic, but it's really just an ultra purified regular oil, and you can run this oil permanently as well as year round. This oil has a much higher detergent base, and also has more ZDDP anti-wear additives that Isuzu lifter's may like.
I want you to also be aware that not all Isuzu engines like all filters, i.e. my engine (which only ticked for 6-8k miles, left as fast as it came) ticks horribly if I put a Mobil 1 filter on, however, someone here has the same engine and his is fine with that filter - so who knows!