Engine lopes and lacks power at start up until it warms up and then it runs fine . What could cause this ?

. Switch to 5W-40 full synthetic heavy duty diesel oil. Only use Motorcraft oil filters. Ensure oil is filled to the FULL line.

. Check glow plugs.

. Change both under hood and under frame fuel filters (Motorcraft only), if they have not been replaced in 15,000 miles.

. Change air filter, if it hasn't been replaced in 15,000 miles.