in the morning a little chugging until the engine warms up then it runs fine

My truck is Lv6 with 210,000 miles on it. sometimes will start rough or not start at all until I clear the fuel rail, it only happens when I shut it off and try to restart it. shortly after replaced injectors it starts no problem. in the morning a little chugging until the engine warms up then it runs fine, but I have also noticed it does not like steep hills. I have replaced the fuel pump and filter. i am thinking it might be an engine sensor or clogged catalytic converters and bad o2s. any ideas would be great.