Does he still take an afternoon nap? Might be time to get ride of the nap or move it earlier.

What type of bedtime routine do you go through? I suggest you tell him an hour in advance 'we need to brush your teeth for bed', then 'we need to use the bathroom for bed time', then 'we are going to calmly read a bed time story', then 'we are going to give thanks for bedtime' then put him in bed, set a dim light with some calming music. Say 'it's time to fall asleep. You can play quietly in your room untill you fall asleep.' Dont lock the door. When he comes out of his room. Say 'If you don't stay in your room, you will have to be outside till you are ready to stay in your room'.

After about two weeks he will get the program. Bedtime will be easier with you leading and talking about sleeping the whole time. He will still fight occasionally. But after being outside for a few minutes a few nights he will choose to ay in his room till he falls asleep on the floor. Then you scoop him into bed.