Your'e most probably looking at fuelpump issues, I had a similar problem with a 2.4 Toyota and ended up replacing some seals on the pump. There is also one filter unmentioned that is located inside the pump, to check it out you have to remove the steel pipe that feeds it. It goes in on the front of the pump and straight down. Loosen the nut and watch out for the 2 copper washers and then pull out the pipe. Deep down there should be a little steel filter wich you can fish out with some solid electrical wire or a skinny screwdriver.

If you have a cold start thingie that could also be playing with the timing advance on the pump leading to loss of power.