Hello everyone. This is my first post on the site. Im having a problem with my 92 F150 4.9 I6 4x4 172,000 miles. I just recently gave it a tune up. I changed the Oil, Oil Filter, Air Filter, Spark Plugs, Cables, and Fuel Filter. It was running completely fine before the tune up, just everything was wearing out, and it was time for a tune up. It runs fine until the truck fully warms up. It is completely fine at idle always, just sputters when im on the HWY trying to go up a hill or whenever I try to accelerate putting it under somewhat of a load. Also when i was inspecting under the truck i noticed the exhaust has rusted through the pipe right before the Cat. Converter. Didn't know if this could be causing problems. Thanks for your time everyone.