Embarrassing Starting Trouble 98 5.0

[yamaha4556]

I have a 98 k1500 with a 305 the thing has a ton of miles on it but runs great. a month ago it started to do this new thing when starting. it starts and goes to 700rpm like normal then dies to about 150 it putts there for a second then revs back up to 600 and idles there fine. sometimes it will even die completely.

i cant figure out wut it is, there are no codes. i thought it might be a fuel issue but i replaced the pump/sending unit and filter last year. i ran some techron and cleaned the map sensor and it didnt happend for a few weeks now it doing again. if i prime the fuel system by turning the ignition before i start it, it kinda helps.

is there some type of a pressure sensor/switch for the fuel system that would control the the fuel pump and were would it be?