I too would suggest you have the computer scanned for trouble codes & post ALL the code numbers found & the sequence in which they were pulled.
If your of a mind to have the tranny fluid changed/flushed, maybe consider having them also drop the pan to inspect for deposit kind & quantity or pan debris, clean the pan & magnet & change the tranny filter, as a pan drop & filter change isn't normally done on a flush service.
So we have to ask for & pay a little extra for it.
As this tranny's service history is unkown, I'd also forgo the "solvent flush" part of the tranny service, because if you have heavy deposits of sludge, gum, tar, varnish, carbon, the solvent part of the flush could loosen too much, too soon & clog something important up.
As I mentioned, with the normal tranny flush service, the pan isn't normally dropped, to clean it or change the filter, so if you don't know how heavy the deposits are, any debris stirred up by the flush solvent & on their way out of the pan, will first have to be strained through the tranny filter, which isn't going to be changed, just further clogging it up. Not a good idea imo.
So consider having them do a pan drop, filter change, refill the pan & continue on with the full tranny fluid pumpout, (minus the solvet flush) while shifting through all the gears, to flush the valve body, torque converter, cooler & lines, might be a good way to go.
This way you'll get a new filter & all new fluid in there wihout the chance of stirring up so much debris with the solvent part of the flush.
The new tranny fluid has a detergent ad pack in it, so it will begin to sloooowly tidy things up inside, so you might get some shift improvement with just new fluid.
Seeing as how you don't know what the tranny deposit load may be, I'd not consider using any tranny additives just yet.
If the shop says things look ok inside after the pan drop & shifting improves with the new fluid, but doesn't completely clear up & you think lingering deposits may be the cause, then maybe consider Auto-Rx for trannies, or maybe half a can of Seafoam Trans Tune & see how things go.
So negoiate the tranny service routine & price. Around here a pan drop, filter change & fluid pumpout is about $150.
Some places will let you provide your own fluid, so that your sure the specified fluid is going in.
Tranny shops pump all kinds of different fluids through their machines, Ford Dealers are supposed to have a machine with dedicated resrvoirs for the different fluids, so they don't get mixed with the residuals of other fluids going in.
The Home DIY proceedure in the WIKI is easy to do & can save about $100, if we do the pan drop, filter change & tranny pump out ourselves. plus we know the right fluid is going in.
A whole bunch more tranny flush thoughts for pondering, let us know how it goes.
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