overheating h1

Need some advise , just rebuilt the 5.7 gas engine in my 1996 H1 hummer , everythings new , new water pump ,  thermostats, radiators clean , fan clutch is new ,  and she still overheats . with out the thermostat she runs between 150 to 220 with gas mileage is awfull at about 3 mpg . Have the timeing at 6 degrees  What I don't understand is how it can run cold without a thermostat and overheat with . Have tried two Napa 190 s that were specked for the Hummer and one 180 runof the mill V8 that fit which worked the best . Any ideas ? what about air lock ? is there something I missed when filling her back up with water ?
Any help would be appreciated .

Have you checked you temp sending unit and guage to ensure they are correct? It may sound odd, but if either one of them are faulty you could be decieved into spending a lot of money. Aslo, is the fan engaged by a bimetal spring in the clutch, or does it have it's own sending unit? It may not be coming on when it gets hot.

as long as ur filling up the coolant system then  burping the coolant system (letting it heat up to normal temp then shuting it off and  after cooling back down filling it up the rest of the way with
coolant)
i would have to agree w/ linus about the bad temp sender or a bad new fan clutch
why did ya rebuild  the motor?
did it run hot and blow a headgasket ?
if so did ya have the head checked
 

Thanks for the reply we replaced the temp sending unit first thing and am going to put a second mechanical guage tomorrow ,  I can actually here the radiator getting hot , it starts to click like an old kettle when it goes to 230 degrees .  today we got some air out of it and siting in the carport shes running between 190 and 225 degrees over a 1-2 minute period . but I didn't take it out for a drive  .The fan clutch was bad and being Costa Rica with no replacement  we welded it solid until I can ship a replacement . Any other thoughts ? any tricks to get out trapped air ?

Kid ,
 
I'll try your burping tomorrow we pushed the hose down below cap level that  helped get out some air  ,
The rebuild came from a low knock that turned out to be a spun bearing but even then didn't over heat , this all started after the rebuild , did have the heads done , new pistons , almost everything is new , runs great other than the heat , have the timeing at 6 degrees what do you think ?

is that a 350 engine? arent those the same as a chevy 350, seems like replacing it wouldnt be to bad cost wise?