Partial throttle tranny slip
 

This started after my indy said my transmission was "shifting a little rough...I will adjust it".

I'm not sure what he did exactly, but I'm guessing the modulator? It sort of hangs at the rpm before shifting, or it slips at 3/4 throttle. At full throttle it does not slip.

I have adjusted my throttle linkage and it made no difference to the problem, only changed where in the rpm range it shifted at. It still hangs for 1-1.5sec at whatever rpm before shifting.

Does it sound the vac mod or something else? I never had any issues prior to whatever he did. If it is the VM, is this something I can do myself or should I really go to someone else to have them correctly adjust it?

Thanks,
Robert

Control pressure cable controls WHEN the trans shifts & the modulator controls how HARD.

Get the modulator re-adjusted to cure the slippage.

Is this something that can be adjusted by feel or does it have to be set professionally?

I read that turning it clockwise raises the presure and going counterclockwise lowers the pressure, is that correct?

Does it sound like my pressure is too low?

MB's Vacuum control of Transmissions mimics ...
 

A Gasser's/Petrol engine manifold Vacuum.
So, @ WOT the least vacuum is presented to the transmission.

All of what I know about Tranny/Vacuum issues is a Mis-translation of STEVEBFL's excellent Tutelage contained here:

http://www.peachparts.com/Wikka/TransVacTune

And here:

http://www.peachparts.com/shopforum/tech-help/19841-transmission-shifting-response-vacuum-span-stevebfl-you-out-there.html#post100041

Of course there's also SMR's :

http://www.peachparts.com/shopforum/diesel-discussion/158216-its-critical-how-you-set-your-transmissions-vacuum-system-your-diesel-mbz.html

DIY link:

http://www.peachparts.com/shopforum/diy-links-parts-category/142395-transmission.html