Just some possible thoughts....
A lot of times, I go with those last...they usually are the shortest cook time & by the time other things (read: meat or heavier, denser foods) are near ready, the coals are less intense, hence, you get a nice settled down heat to cook with.....
the meats & such can be either taken off or set to the coolest part of the grate to sort of 'hot hold' while the vegs cook....
Here's a whole dinner on an 18"......shows, kinda, the sequence or rotation to get things done up together......
http://weberkettleclub.com/forums/grilling-bbqing/previous-don't-really-need-all-those-kettles-just-one-18-12'-5/msg7900/#msg7900A thing BBcue-Z was talking about the other day made me stop & think.....vegs are mostly water so they get treated differently when cooking.....
http://weberkettleclub.com/forums/bbq-food-pics/grilled-chicken-wwhite-bbq-sauce-and-lamb/msg148130/#msg148130Here's another of his....this fine fellow is quick with the tongs, I guarantee ya.....
http://weberkettleclub.com/forums/bbq-food-pics/horseradish-steaks/In looking at his stories, you'll a lot of times see the vegs on a different grill or an area setup up separately on a grill also......that can help.......
Here's a demonstration of concept:
All the coals are under the meat-based skewers, the shrimps are still in the heat & will cook, but need much less.....
I'll use a 22 for main stuff & 18 for vegs & accessories quite often.....
One other thought might be...what are your coatings / marinades?
Some things with olive oil will tend to burn quick....maybe test out herbs / spices with little or no oil just to see if it gets you a better handle on it.....