weird idle help needed

[Accident prone]

ok to start 97 ranger xlt 2wd 4.0 115,000 miles
things i have replaced, plugs- ngk, wires-bosch, iac twice cause i thought the first one was defective, cleaned maf multiple times with proper cleaner, modified air box with k&n filter, oil change with k&n oil filter, vacume lines to carbon canister, new 130 amp altinater,

now the problem, weird idle after it warms up it just bounces between 400-600 rpm, both lean codes 171,174. stalls sometimes when hitting brakes or making hard slow left turn or going into reverse ( note does not happen all the time) headlights dim when hitting brakes at low rpm, ( i installed a amp therefor i installed a heavy duty alt, ) bad fuel econemy

any ideas would be great, sorry for spelling