that temp seems a bit low especially since you have the 190* tstat. i was having trouble with mine at first but it was overheating. so i was driving without a tstat for a while which let it basically run around 120* came to find my problem was that i only was filling the rad and not the block (like you mentioned you already did) so thats not your problem. once i filled the block, it does not go past 190-195 which is where you should be too.

what are you getting your readings from? your old 89 gauge? if so why arent you using the stock SENDER for that gauge from the old motor? then you know it will be accurate. if you have a decent scanner, you can also get the readings from the computer which uses the LS temp SENSOR. i compared my scanner to the cluster gauge and it was almost spot on.

i know im not being too much help, im just giving you some food for thought. but if i was you, i would just use the stock sender and be done with it. you know it will show the accurate reading on your cluster. but this should def be sorted out soon cuz obviously getting too hot could kill your new motor. but im glad to hear you got her running! and i agree, the LS on its worst day is better than a tbi on its best. ha!