Truck needs to be jump started every time

Once started it drives great. Good power and headlights do not dim. If I turn it off and try to turn it back on again right after it cranks a few times, but doesn't start or just barely starts if I'm lucky (usually it doesn't). I have replaced the battery, alternator, starter, and diode recently, but it still needs to be jumped. When I turn the key it tries to start, but it doesn't want to due to what sounds like lack of power to crank starter. The only other thing wrong that I know about is that the driver's side front blinker recently stopped working. The blinker circuit blew the fuse for a couple days, but has stopped blowing fuses. All other blinkers work. I discovered no juice is getting to the drivers side front blinker filament in the new two filament bulb I put in, but the running light filament does work.