I think this was a mid-90’s Toyota pickup, right? I had a Toyota pickup once and it had fuel starvation issues at freeway speeds. It ran fine otherwise, but would often have a fuel smell. Turns out the lines on the fuel pump had been reversed by a previous repair job. If I recall correctly it was the lines coming from the fuel tank to the fuel pump and cannister that had gotten reversed. It was trying to draw in the vent line and vent through the fuel intake line. Interestingly this was enough fuel at low speeds to keep everything working, just had problems at high speeds.
It could be that the mechanic pulled the fuel lines to clear them and then put them on backwards. The only way I figured out the problem on my truck was to pull the lines and stick the air compressor nozzle on them one at a time. I was troubleshooting it as though it was a blocked line, and was surprised to hear the air coming out of the wrong place. Might be a similar issue here, if the mechanic hooked them back up wrong after removing the “mud chiggers”. (I suspect it was a different source of fuel line or vent hose blocking, but either way the same mistake could have been made.)