I recently had several items at on my 98 GT
1) Replaced 4R70W fried transmission with a Lentech Street cruiser with stall converter
2)Changed stock gears with 3.73
3) Bassani catback.

Since these upgrades I get a flashing O/D Off flashing light. It only comes on when I cruise at highway speeds. It eventually shuts off after a couple of starts and "city only" cruising.
The transmission seems to be operating perfectly, the light just comes on, and eventually goes off.
I went to Autozone to get them to pull any codes (while the light was flashing), and here is the weird part, there are no stored codes.

Doesn't a flashing O/D Off light generally generate a code in the computer?
Could the gear change be the culprit instead of the tranny?
I am at a lost here, and any information is appreciated.[/align]

 

well this just happened on my car and normally on automatics when the overdrive light flashes its like a check engine light for the tranny i would check ur tranny

 

Mine did that a few years ago. I just took it to the stealership and they reset something. Hasn't done it since

 

Flashing O/D off light indicates a problem with the automatic tranny. Since you no longer have the stock one, it's probably just the computer trying to figure out whats going on. I say unplug the sucker!