The ECM does need to get some miles on it to 'learn' the new engine. And maybe this motor is still tight and will 'loosen' up after 500-1000 miles or so. Your other worn-out 3.4 would have had very loose tolerences and likely pretty low internal friction as a result.

My 3.4 was also doing some of that stalling and it's pretty much settled out after re-adjusting the idle air and TPS voltage. I still need to get my 2-1/2" exhaust put on to get the motor uncorked, it's strangled like crazy past 4500!

Keep us posted on how it's running.........ed

'90 Troop 3.4 LS
'89 Troop RS (Has Valve Issues, needs Counseling)
HI, I'm Ed and I'm a Trooper-holic!
Keep On Troopin'......