[cummins]

i have a 2000 excursion driving me crazy, first start in the morning it cranks for a while before it will fire. when it finally does it runs with a miss, enough to stall it if you try to pop it in gear before letting it warm up, there is some white smoke during cranking, but just a litttle, if i plug it inover night , it will fire right up. after 5-10mins it runs perfect, no miss and it will fire up all day with 1 crank. i had a bad glow plug module, it was dead, i replaced it and it now works, but makes no difference on startup. so i pulled the valve covers, checked every conection and plug on both sides or the valve cover gaskets, no melting or burn marks. i checked for power at all 8 conectors to the glow plugs, and they are fine, stayslit for 2 mins. while i had the valve cover off i replaced all 8 injector o-ring kits with the latest ford part #'s and all 8 glow plugs anyway. i also replaced the ipr orings, the fuel filter and drained the bowl. all this made it run a little better, but made no difference on startup. i also replaced the cps, because it was cheep with a new ford part, and i had a spare idm and lift pump, so i swapped these out as well, makes no difference, i have done a couple of buzz tests over the last month and the first two and the last one sound weaker then the rest, but they do not pull a code. i have not searched which cyls these are yet, or on which side yet. it does fail cyl8 contribution test, and i am leaning twards injectors, but i do not want to throw any more parts at it. i want the next part to fix it. the truck does have 250k on it, but warm or cold it has no blow by from the oil cap or dipstick, i bought a harbor freight comp tester to to a comp test when i did glow plugs, but it will not fit between injector and pushrod. truck uses no oil, leaks not a drip, and gets 23mpg on the highway, 17 around town, so i do not think the motor is worn. shoule i replace all 8 injectors if they are the culprit, or just the bad ones, anyone have a good inexpensive source for injectors? are there any further tests i can perform?

PLEASE HELP ME!!!