Borg Warner 35 Advice

[Puddles of Oil]

I have a 1592cc Sunbeam Alpine Automatic from 1965 fitted with a Borg Warner 35. This gearbox was really common in old classics and was put into MGs, Rovers Triumphs etc.
I have had the car for 20 years+ but I am certain that it is slower now than it used to be. At about 55-60mph it is getting quite frantic and is not pleasant on the motorway. When new this car would do over 90 mph, if I tried to do that now the engine would go bang before it got anywhere near that speed!
In top gear the drive is 1:1.The engine is in good healthy condition and I think if it was a 1600cc manual being driven at 1:1 it would be MUCH faster.

My query is whether there could be something in the automatic gearbox or torque converter that is causing a loss of power between the engine and the drive wheels. I'm thinking could it perhaps be a pump not creating enough pressure, a valve releasing incorrectly or a drive band slipping or something like that? All of the gears seem to be engaging correctly, the car pulls away in first goes to second almost immediately and then into top at about 15-20mph which is what the manuals says it should do.
I am pretty good with manual cars but automatics are quite alien to me and I would appreciate any advice or help that anyone can give.

Thank you,

Oily

[Puddles of Oil]

Thanks for the replies. It has Ford ATF in it which is correct. The Rootes manual says that the fluid should NEVER be changed (but it has been previously and has not had an incorrect fluid in it, at least not for the last 20+ years). I know of people who have only had problems after changing the fluid because there is friction material suspended in tel fluid and when you change it for fresh fluid you get problems.

I was hoping that someone might know a specific thing in the box that could cause it to lose some of the power. I am pretty certain that it used to drive faster at similar revs in the past.

I will try and get a specialist to look at it.

Oily