Lumina heat and transmission (1999)

Hi there!

(1999 Lumina Sedan 3.1, 116,000 miles.)

My questions are:

1) Occasional hard shifting in and out of 1st gear. Had fluid replaced at 85,000 miles as it was dark and a fair amount of chips. Had fluid replaced again, another shop at 105,000 miles. No check engine light or other problems. Fluid was not leaking at any time. Mechanic mentioned fluid was a little dark for being changed that recently. Very little chip contamination. What else can I try?

2) During cold temps, like the morning commute, I get almost no heat. The gage shows about 1/4" over the 100 deg mark for the whole 30 mile drive to work. The drive is highway speeds most of the way in. There is heat when the weather is warmer, or if I'm in traffic conditions. Had thermostat replaced in the summer, after temp gage was observed moving all the way to the red line, then as it opened up, I got heat and it indicated normal operating temps. Coolant was dark brown and had thick, sticky globs in the radiator cap. Drained and refilled coolant system (and broke stupid plastic drain valve in the process). Had intake manfold and valve cover gaskets replaced at 95,000 miles due to leakage, as I understand is a common issue with this particular engine around that mileage/age. What else can I look for? Is the thermostat defective, sticking open and keeping the engine cooler?

Thanks in advance.