Hey Rick....
I've got the 3ltr ZD30 ('03 model) that's also chipped and has the bigger exhaust and Intercooler installed and I've only had the car since the 1st part of the year and I've finally gotten around to towing our 17" Windsor Rapid Van up to the Sunshine coast (twice). The 1st time I was disappointed at how poorly these 4cyl 3T towing capacity vehicles are geared in 1st gear. This is also across different manufacturers aswell so I've been told (unless u happen to have an Auto).
Our van runs around 1800kgs unloaded and I'm only running the std tyres at the moment (255/70/16). On take-off with any slight incline is the issue.... once you're up and running everything is fine and it goes/pulls great. If there was a way to install a lower 1st gear on these D22's, then everything would be fine.
My 2nd towing experience over the recent christmas holidays went better as I added more right boot on take-off, but I can now understand why u hear of so many people who are burning out their clutches so quickly with these and also on the more modern 4cyl Diesels with high output..... Our 150's Prado which is a D4D Auto beats it hands down in the towing department, but so far I've gotten better economy out the D22 even though it's only been straight up the highway and didn't really include going over any mountain ranges, etc......
hope that helps a bit.....