1997 1500 ram problem

[bluebuick91]

i can drive it about 20 miles and it starts running bad enough to stop. but if i sit there letting it run bad at idle for about 5-10 minutes it will start running good, then i can go for about 20 more miles and do it all over again. any clues

has new plugs,wires,coil,cap,rotor, fuel pressure was 50lbs,injecters checked out ok,

it does get around 210 degrees is that normal

also it is a 4x4 and the front axle on passenger side there is a box that has a switch on it and it looks like it is bolted but it is leaking gear oil how do i fix the leak i know if i remove the box i can change gasket but if i pull off box will a spring or somthing come flying at me orhave parts fall out i can't get back in, any one have this problem and know how to fix it thank you