GMMERLIN-fuel sensor fixed -- now the tranny

[hubbie]

seems I have two fuel tanks, replaced front fuel sensor, gauge still NFG, replaced "rear" fuel sensor today. Geez, since I have only one fuel filler cap, and no way to change over tanks, I always thought I had only 1 tank. I'll have to crawl underneath later today to find this "second" tank. Next problem, when I manually place the auto tranny in 1st, at about 2800 to 3200 RPM the tranny shifts up to 2nd, and occasionally 3rd gear. If I let off the gas, it will drop back into 1st. Diagnostics indicate the "computer" is commanding it to do this. I always thought if I place the shifter in 1st it should stay there. BTW, if I am in "drive" and punch it, the tranny doesn't shift until about 4800 RPM, and it won't downshift into 1st unless I am going really slow. GM rep still head scratching on this one, and indicated it may be a software problem that I have to live with. I didn't spend $55000 CND to live with a software glitch. Any suggestions??