Help with 84' Chevy 1500 Trannie

I have a 1984 Chevy 4WD, 1500. Auto transmission.
I've never had any problems with the truck except for normal
maintenance.

When I pulled from the house today the transmission when it started
to
shift felt like it was slipping.
After about 4 miles when going up a hill I heard a 'pop' underneath
and then lost power.


It had no forward but I could go in reverse.


I looked at the linkage and all appears to be working alright.


That's when I noticed a leakage coming from the left side of the bell
housing.


A check of the fluid indicated that it was low and I put more fluid
in
(level ground).


It still would not engage in forward..it would engage in reverse.


Question:
Does anybody know the type of transmission that is used on this truck
in case I have to get another one?

Could it be just the torque convertor?


Is there anything else I can do to check it out except for dropping
the pan on the trannie?
(I know it's an old truck but I've had it a long time and I like it
and take care of it.)


Thanks for any input or advice.


Josh