7.3 wont start
 

hey im new to the 7.3 and i cant get my buddies truck started up.its an 02, he was driving it and the starter went out. replaced the starter and now it wont start. he was running it off of starting fluid but cant get it to run on its own.and the abreviations on all this are killing me. any help would be much appriciated.

Does he have a manual transmission? if not don't scratch that. did you check the batteries? how old are they? the last question did you check the connections on the starter? there is going to be more questions. PM me if you need to.

it cranks and cranks but it wont fire

my other buddy with a 7.3 and it runs like crap and you have to let it run for about fifteen minutes before it will pull itself. and when you go down the raod it dosent really have power and if you down gear to slow down the thing goes back to where it wont pull itself again i have to sit on the side of the road and hold it to floor till it makes it through the rpm range, and it takes a while then it will putt on down the road with almost no power. guys i need help because he needs his truck to move and i cant figure out whats wrong with. please help