loss of mpg and truck dying

[Gib]

I am new to Powerstroke and website with a lot to learn.

I have been driving a Cummins and recently (2 weeks) switched over to Powerstroke. It is '01 F250 4x4 with 123,000 miles on it.

First tank of fuel with no pm resulted in 15 mpg.

PM oil, air, fuel, antifreeze, water pump, and belt. I went up to almost 18 mpg. I then pulled a light, aluminum boat around in some wind and dropped to 15mpg.

I am now at about 11 and 12 mpg and the truck has died on me 3 times unannounced but always starts right back up and off I go with no problems. Scary stuff. It also "burped" on me one time.

Any suggestions on where to start?

One more thing, I have manual locking hubs and a switch inside for 4wd. Previous owner told me if truck would not go into 4wd by turning switch because sometimes it will not, just get out and lock hubs, and then turn switch. Does manual and switch work independently of each other or must I lock hubs on outside before turning switch?

I appreciate the help and any insight you can give me to make me want to keep a Powerstroke.