After a lengthy rumination period I finally took the leap and did the DIY version of this process where we completely exchange older ATF for new. I've heard the myths and horror stories of complete transmission fluid exchange causing premature failures etc but after reading a few comments by Mr Mark Kolvolsky on FTE it didn't seem to be nearly as dangerous as feared or described. (It didn't hurt I finally made connections with a local customer/friend who'll completely rebuild a 4R70W for about $400 with another $300 cost to R&I the trans if vehicle is towed to him.
I did this complete this past weekend on the daily driver work van with 211K+ miles on the clock. This particular transmission had previously been serviced with the typical 5 qts + filter at 80K miles and again at 172K miles. I have another E250 with 275K miles on the original transmssion I'll be doing this same exchange on soon---its running so well $110 for a bit of upkeep is pennies all things considered.
The process is super simple, can be done with just one person and requires very little in terms of tools: 10' 3/8: clear tubing, pliers, screwdriver, hose clamps along with a suitable 5 gallon bucket or container. Apart from storing spent fluid we need to know how much ATF has been removed during the different steps a single-person operation entails. Naturally new ATF and a filter are required too.
First thing noticed after completion is a greatly reduced time for the transmission to engage after a gear is selected by the shift level. After 50K+ miles driving this transmission such a comparison is easy to make. Test drive reveals a smoother shifts both up and down, not a bit of lag that might be attributed to the trans itself rather than the PCM strategies.
Overall I spent $110 for fluid + filter from the dealership no less---they had the best price per quart on the ATF, filter pretty much normal cost if obtained elsewhere. Having spent several months searching for best prices on the ATF it was on a whim I called the dealership---was shocked they were best price.
Here's Mark's article on the how to: http://www.ford-trucks.com/articles/...-transmission/
. There are a few minor differences when done on an E-Series however they're almost insignificant in the overall. The only real thing to know in advance is its best to have at least 15 quarts of ATF ready even though his recommendations the 4R70W's require only 13. My own experience shows 15 is needed, having 16 standing by wouldn't be a bad thing.
So anyway I'm a full convert now on a job not much more complex than an oil change or coolant replacement. I might do a small write up but honestly don't know how to improve on Mark's article. Anyone with specific questions about this process on a 4R70W in an E-Series chassis I can help---any other transmission in any other vehicle or chassis I'm NOT the guy to ask!