Ive got an 99Expy EB w/ 185000 miles and for months its been hesitating esp on long hills and it seems to not hv as much power as before
Thought it would throw a code(like when a COP/plug is bad) and it seemed like the same issue(i hv replaced 3 Cops now)
Kept trying to hammer the engine to get it to gv me a code but it would just never happen.
The other day I had to replace the starter and started to see if i had any vacuum leaks since i know the triton 5.4 is famous for those
Found one hose that was totally off and plugged it back in and the engine seems to run better w/ much less hesitation(still some) and more power
Sure enough the next day it finally throws a code....0174 too lean....but is still running better

What could it be?

Also my heater/AC unit is acting up......for awhile when the AC was on it would switch btw def and vent and back w/o any buttons being pressed
Now i cant get the AC to come on at all.....sometimes it will if i turn the key off and back on

Do i need another temp control unit and if i do is there any manual to walk me thru it.........my haynes manual says nothing about the temp control unit

Thanks

 

All of the symptoms you're describing are typical of a vacuum leak.