Car won't run past 60mph

Guys,
Here's the deal my 360/727 with a 2.76 rear gear is running 4,000rpm topping out at about 60MPH. It pulls like a freight train getting there. But with the 2.76 I thought for sure id have a high way cruiser. I have 318 heads which I know is choking it out on the big end. But even still I shouldn't be running at such a high rpm at 60mph. I think it may be a trans issue. I do have all three gears shifting fine. This drive train did come out of a RV so I was thinking is there a limiter or something up with the stall converter. I was going to try and do a basic service on it with a new filter and adjust the inner and outer band. Shifts somewhere around 15-20mph to 2nd and around 30-35 for 3rd but then revs out from there.