Yo Carlos,
Welcome!
Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19
http://broncozone.com/topic/14269-code-reader/?pid=74587&mode=threaded
Helps to have someone else assist in this test.
Some basics;
The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.
Run it around to heat the engine up and shift thru all gears including Reverse.
Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual & release clutch.
Then turn off engine, all accessories/lights (close driver's door) , etc.
Do KOEO test First
Post Code(s) here according to:
KOEO
&
KOER
...
Without a code to narrow down the troubleshhoting, this problem could be caused by a # of things;
bad vehicle speed sensor (VSS) (also called ABS,, DSS sensor) on the 8.8 (rear differential)/ or Connector/corroded wires inside connector;
or cruddy/damaged tone ring in the 8.8;
bad 4WABS Module - It is located below ws wiper fluid/coolant recovery tank. So, the connector can be corroded by leaking fluid;
bad PSOM (Speedo);
bad wiring/shorts /connectors from VSS at firewall, at 4WABS Module and /or at PSOM and then onto the PCM.
If neither a voltmeter nor frequency counter is available, vehicle speed control may be used as a good indicator. If it works normally, then the speedometer module is at least receiving a speed input signal and the wiring and sensor & tone ring can be assumed to be good.
