i have noticed when i go up hills i start out fine but than i start slowing down.I keep constant pressure on the pedal and the truck makes a loud thump and starts going faster.I noticed the rpms go up to about the mid 3 to 4 range.Any info on why this would happen?I cant afford to have to replace the tranny.I just had a spark plug blow out of the side of my engine so i dont need any more bad news.
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1999 f-150 5.4 liter triton 2wd 4 dr p/w p/l tilt wheel,towing pkg.

super cab styleside bed maroon
16 inch rims
jensen cd player 5 preouts
2-1000 watt pyramid subwoofers
2400 watt amp.
bug sheild,bedliner,tail light covers,windsheild nozzle lights
blackouts,dixie horn

Future add ons
Lift kit with 35 inch tires
dual exhaust
moon visor
maybe some strob