My 2003 will start when it's cold but when excellerating,the rpm's will not come up until about 2 or 3 miles down the road.After that it runs fine.Can someone please give me suggestions?

 

Scan for codes. Report back.
Look into the scan tools that can read live engine data (scangaugeII is one, there are phone apps also: Forscan, Torque). All 6.0L owners should have one.

In the meantime ............

check oil level
post what oil you are using and how many miles are on that oil
make sure your batteries are fully charged and your connections are good, tight, and clean.
personally I would have the batteries individually load tested also