99 f250 sd trans problems

We have a 1999 super duty with a 7.3 turbo,auto trans.when the truck first takes off it is fine,but after the 2nd time it shifts,it shifts really fast,we have done trans service,the fluid was clean.brought it to a trans shop and they told me it was the computer,put a new one in at the tune of 265.00.did not help,the trans shop told me that the computer was not communicating with the trans.maybe a broken wire,I have no idea where to even start with this and I don't want to keep driving it with the chance of wrecking the trans.Thanks for any help

Run scans for stored error codes & pick up a repair manual. My truck is pre- computer controlled but I believe their are gear shift servos that go bad. Your Running or Continued Memory errors should I.D. the bad servo & the manual will show the location and method for replacement which should not be very difficult. If after replacement if proper shift isn't immediately restored, disconnect the battery for at least 5 mins. then reconnect which will clear the KAM (kept Adaptive Memory Learn Tables) and will reintroduce the functional servo to the computer while the tables begin rebuilding. Drive smoothly w/ mild acceleration thru shifts for the first few miles while it re premises itself based on how it is driven. Your tranny shop bent you over telling you your PCM was bad. If it was the problem, that also should show in an error code or no scanner communication at all. CEL's (Check Engine Lights) are not prerequisite for error codes to exist or to be stored in Continuous Memory unless it's more specifically emissions related.

The scanner did come up with no comunication to the trans.

The scanner did come up with no communication to the trans.I would disconnect each electrical connection. clean both sides w/ electric contact cleaner, inspect each connection wire and check that none are backed/ pulled out the back of the connector setting to far into the connector housing that when joined , the wire isn't making contact.Trace wires looking for damage sometimes a wire will stretch and separate but insulation remains in tact, it will look and feel thiner. The manual would supply the wiring diagram. That circuit might have its own separate feed which could mean that a fuse or fusible link might be bad. A bad VSS can cause these symptoms but I'd expect a code for that rather than the one your getting. After cleaning & inspecting, turn key on and test for power. I would think 1 wire in each connector would show voltage to ground, and another should show continuity or a resistance to ground if the return path is by way of the PCM. As I said, my truck tranny & PCM couldn't care less what the other one's up to so my personal knowledge is remiss, but I thought you might get lucky inspecting and performing some of the basic troubleshooting tasks and find the problem that you'll pay $75/hr for a shop to do. W/o a schematic I'm limited to guesses. P/u a manual. you should have one anyway. Another option is a subscription to Alldata DIY- http://www.alldatadiy.com/about_alldata/index.html for your specific yr/model truck. Factory repair info. $30/yr. could have paid you up for 9 yrs. instead of having an extra computer laying around(you can recoup some of the $ selling it on Ebay):banghead: Alot of repair shops have pro subscriptions W/ unlimited access for all cars, but employees are too lazy to use it & selling only parts that are actually needed cuts into thier profit. A benifit after haveing a sub for a year, even if you don't fix things yourself, you'll know right away if your mechanic is talking out of the correct oriface and It also includes labor time & parts required for any repair.