This is my first post so here we go.. I have a 99 Grand Prix GTP.. Bought the car with a blown motor. After replacing the motor car has ran great until today.. car drove fine into town, stopped and got gas and thats when my day turned to crap. The car hesistated when I left the station, acted like it was slipping.. finally found second and then promptly coasted to a stop. It made no noise no nothing.. honestly acted like I put it in neutral.. after setting along the road gathering my pride for twenty minutes or so, I found that in reverse if I reved it to like 3 grand it would start to shudder, make some grabbing noises and take off backwards like a rocket. If I would stop and quickly shift to first the car would move. If I kept the motor wound up like 3 grand it would stay moving in first.. still no noises..and no signs of slipping.. when I would come to an intersection I would keep one foot on the throttle and power brake if you will keeping the motor wound up and eventually I got the thing home..

Checked the fluid.. looked good.. full.. no bubbles..
Dropped the pan.. no shrapnel or "glitter" or anything that screamed "well theres your problem!!"
New filter and fluid just for kicks..

Car will not move unless you rev the heck out of it.. and when it decides to lock up and go its in and gone.. so long as you dont let it out of first its good.. I have read like 10 pages of forums on here so far and havent came across anything like this.. I have killed several transmissions in my time and generally its pretty obvious something bad happened.. but honestly I have never had one act like this..

I am thinking either the torque converter or possibly the pump?? I realy dont want to buy a whole other transmission and start over if I dont have to.. I would much rather fix this one but at this point I am open to about anything.. Any help here would be greatly appricated.. and Thanks in Advance!!