C60X running not as well as it should....

[warren brown]

Hi everyone - had to move the C60X to our new house (about 40km) and for the first time since I've had it the truck was struggling up hills - or under load. At idle it sounds fine but it develops a chug - as though it's running on five cylinders and runs out of puff. Normally it lopes along pretty well - it starts and idles very well but once you give it a few herbs it doesn't sound quite as smooth. I'm going to remove the plugs and leads and probably replace them - and have a squizz at the distributor cap in case there's a crack - I hope it's not something catastrophic but I'll start with the simple things first. Are there other things I should check I haven't thought about? Does anybody know what size spark plugs they are for the GM c60X engine and any tips on plug removal before I start dismantling the cab? Cheers and many thanks - Warren