Oscar, and red texas, are really not great suggestions for a 55 in my opinion. They will just get too large. And the Red Texas (actually a flowerhorn type) are known to be highly aggressive, could definitely kill the pleco.
The cichlids I mentioned could probably work with the pleco and barbs. None of them get all that large. They all can be quite aggressive, so there would be risk. But hopefully they don't see the pleco or barbs as a threat.
Here is a video of my male panamensis in his 45 gallon planted, where he is the only cichlid, but lives with smaller peaceful fish. It should be noted he has taken out some of the slower residents of this tank, since introducing him. Barbs and pleco would probably be better than the fish I have with him.