hey guy- ive gotta 92' deville (4.9) that does(did) the same thing...... i took it to a certified tech and found that the problem is in the fuel injectors themselves. apparently the injectors were only holding a very low resistance causing them to function poorly. the proper resistance is around 15 ohms. you can get a replacement set of refurbished or slightly used injectors online for around $250-$350. from what i understand (youll wanna check this in detail) you can also use the injectors off of a 305 Camaro TPI which you can probably get for around $200 online...................Good Luck

 

after driving my 94 Deville from mechanic to dealer to diagnostic center I found the following
1) the stutter did seem to improve by leaving the fuel tank full and the cap loose
2) the stutter only happened after the car was on for aprox. 15 -20 minutes
3) by kicking the gas at the right moment I could over come the proplem occasionaly for a few minutes
in the end it was the replacement of te hall effect sensor in the distributor of the 4.9 engine that fixed it
since then I have put 80000miles on without a problem