96blazer w/94LT1 no communication w/scanner

Dropped a 94LT1 in my 96 S10 blazer. The wire harness from painless proformance came with it's own obd-ll connector but my snap-on scanner keeps saying there is no communication. painless said to switch the 30-pin to the 29-pin location in the blue computer connector but it still says no communication. Checked all the ALDL pins with a volt meter and it all checks out fine???????????????????????????????????????????
I even tried a new computer. the engine runs a little rough at idle and power cuts in/our going down the road. any help would be great.
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94, that is an obdI computer, not obdII, unless youve got a typo that is why theres no communication