What unrelated lights might show up if you have a weak battery? I remember someone mentioning something about this at some point.

 

S/m blinks limp mode
3 amigos possible too (at least that was the case for me)
I'm sure there are more

 

x1 ............ if the cold cranking amps (CCA) are down it causes the ECU's to 'throw a wobbly' and various emergency warning lights can appear as Dusty says. Worth an amps load check on the battery by an auto electrics garage or someone who knows what they are doing with load test equipment.

A quickie check is to put a voltmeter set to 20 volts DC across the battery (NOT AMPS FFS) and then get someone to crank the engine on the key. If it shows 9 volts or less whilst cranking the battery is usually defective. This is not a totally definitive test only a very quick indication of the battery state.

 

sometimes the tach will also fluctuate

 

I just had my transmission heat sensor come on again, it came on a few months back here and there, and then went away, and now it is back again.

I am planning a 3 hour drive coming up and I need to make sure my truck makes it there. I get nervous now as I have been used to problems popping up at the wrong time..

 

Was engine warm or cold. Those things can go bad. I replaced my temp sensors for that reason. Easy swap but I think it was like a hundred bucks in parts.

Both t case and tranny cooler sensor, command that light. If you get a chance you can quickly unplug one or both the leads on the tcase next time and that will determine the sensor at fault.