Help. I need Oscar advice. I am fed up.

Here is my setup:
75 gallon long (5 feet long x 1.5 feet wide X 16" tall):
1 Albino Oscar (10.5" including tail)
1 Sunshine Pleco L-14 (8-9")
4 Silver Dollars
2 Fluval 404 canisters, 1 Maxi-jet 1200, weekly water changes.

I am very attached to my Oscar and Pleco. I have tried other cichids in with my Oscar with no luck. First I had a Blood parrot he grew up with and then turned on a year and a half later. I removed the BP and put a Jack dempsey in instead. The JD was too aggressive for my Oscar. So I took out the JD and tried a Severum. The Oscar beat up on the severum too much so I took it out. I thought forget it, I will just leave the tank with the Oscar, silver dollars and the pleco. Now, my Oscar seems pissed and it chasing after the silver dollars and pleco (which he never did before). No damage has been done, my pleco just hits him with his spikey fin. Will the Oscar settle down? My only other thought would be to try adding a 3-4" convict and see what happens, but do you think it would beat up on my Oscar or pleco when it gets bigger? I am not able to get a larger tank (on a second story and tank fits in a nitch in the wall of my living room), so that is not an option. I would like to keep these fish forever so I don't want to add too much so they would overcrowd when they are full grown. I am willing to remove the silver dollars if necessary, but I do not want to part with the Oscar or pleco. Please tell me what I should do. It is also very difficult to find larger cichlids other than convicts in my area.

P.S. Sorry for all of the compatibility questions. I am sure you guys are sick of it..........but I just don't know what to do. Probably the best thing for me to do is to take a valium and stop worrying so much.

It seems like there is a lot of space in there since the tank is 5 feet long instead of the normal 4 foot. Do you think he will hurt the pleco? So far the pleco seems like it is standing up for itself. He is alway out now that the JD is gone and doesn't even go into his hiding spot when the Oscar pokes at him. The pleco usually hits the O in the face before the Oscar actually does anything to him. So do you think he is Ok for now? The silver dollars don't really seem to mind the Oscars little chases, and the Oscar is not actually biting them. Do you think this is just because I removed the severum today and it is his first day (in over a year and a half) being the only cichlid in the tank. Do you think he will settle down over time? I really want to keep the pleco. I just love them both.

The Oscar is about 10-10.5" and the pleco is about 8.5-9". They have been in the tank together for about 6-7 months now. Before that he was in the tank with some albino bristlenose plecos, but I removed them because I was worried that he might eat one since they were only about 3.5-4". The Oscar is about 1.5 years old.

Here they are.......I can't bear to get rid of one of them:

After watching them for a while, I think they will be fine. The good thing is that there is no fighting after the tank lights are off. The Oscar just goes to sleep. Before the Oscar and the other cichlids would fight when the lights went off. I think I will just leave the tank alone for now and see what happens.

Thanks for all of your replies. I think I am just being a paranoid mommy. After all this is my first cichlid experience (I have had him for 1.5 years and have only been keeping fish for 2 years). I don't think I could handle having a more aggressive fish. I would just be worried all the time. I bet if someone else was watching them they would think I was crazy and had the most mellow Oscar.