I have a few questions and descriptions of conditions about my
automatic transmission I'd like to get answers to, in general terms.

I have a Dodge 3/4 ton B250 van, 318 cu. in. engine.  The 3 speed with
overdrive on the column automatic transmission has been rebuilt and
'stiffened/heavy duty parts installed' about 2 years ago by the
previous owner.  Here's some descriptions and questions.

The trans. is slow to shift upwards in the gearing.  Low range  really
roars, and I have to gently let up on the accelerator to get it to
shift up.  It then winds up again, usually, and I need to do another
but smaller let up of the gas to get it to shift up into Drive.  It no
longer will go into automatic overdrive, but remains in Drive.  That's
great for the mountains and hills around here, but still something
that isn't working properly.  lol  Other than the aggravation of
having to help it shift, the rest of it is fine, no grabbing, jerking,
slipping or any indication of anything wrong, other than the poor
upward shifting.  It does this harder when cold and easier when warm
and run a while, but is still winding out pretty good in the shift
from Low to D2 to Drive.  I don't have a tach, so don't have any
reading of that, other than feel and ear.

Questions: Number one of course is what is the possible problem
(problems), number 2 is the possible solution?  Third is how expensive
will it be.  It seems to me that this isn't a transmission problem, in
the usual sense of transmission problems, as there is no evidence of
gearing damage, etc.  just poor shifting.  Am I wrong in thinking it's
something outside the trans. gearing and bands itself, maybe, such as
a regulator, valve or such?