ok i have a problem,lol 99 f 150 4x4 4.2 5 speed... check light does not even come on but check codes and i got 02 sensor bank 1 and bank 2 and both lean..ok soo i change both sensor and still got the problem..also could be map.well change that as well the problem is if a floor it over 3000 rpms it hesitate and not go..now seems to have a slight it got alot better i was wondering if you have to drive it alittle to fix it self? any ideas?

 

Changing O2 sensors usually does nothing for lean codes. Check for vacuum leaks and clean the MAF sensor. When was the last time the fuel filter was changed and has other maintenance been done regularly?

 

fuel filter yesterday,and brandnew map yesterday! l seafoam the tank and intake! umm i was told might take sometime time for the map to fix the problem but i'm not sure?

 

The seafoam won't do anything to help (marketing and placebo effects are the only gain). Look around the base of the throttle body. 4.2L like to get leaks in the gasket there and can wreak havoc. Also all vacuum hoses too.
Can you hear the fuel pump running and have fuel pressure?

 

yep fuel pump turns on it runs! just still acts up! it got alot better but still has alittle hesitate not as bad as before also sometimes now has bad start up..but if you restart it,it starts fine? but i check for leak and whats the reek havoc?

 

Probably when it's restarted the motor is warm and lessens the affects of a vacuum leak. Havoc: great confusion and disorder, according to Websters.

 

Buy a can of brake clean and spray around the upper and lower intake gaskets while the truck is acting up. Do not do this on a hot day with the truck hot as well being that it is flammable. If the roughness straightens out then you've got yourself an intake leak.

 

only does it with the motor on a load not a idle..could i have a weak fuel pump that just has not gone out?

 

Hmmm... it does sound like a fuel filter but you said before that you had already replaced it... Possibly the pump getting weaker and not being able to supply the higher demand of fuel under heavy load.