[shorod]

I'd start by giving it a good tune up, specifically distributor cap, rotor, spark plugs, and spark plug wires. The symptoms you describe are pretty common for a cracked distributor cap - moisture gets into the distributor through a crack and shunts the spark to ground through the condensation rather than through the spark plug wire and plug. The car may idle, but as soon as you put a load on it, it misfires horribly bad and stalls.

If that doesn't fix the gear change issue, then you should check the condition of the transmission fluid. If the fluid is badly burnt, it could cause the pressures to be off, effecting the shifting. Or, you may have a vehicle speed sensor (VSS) that is faulty.

-Rod