02 duramax w/allison trans threw a P0776 code truck would not pull forward unless in 4 wheel drive. Made clunking noise when put in drive from park. This is apparently a b solenoid but where is it located and could it cause the vehicle to not be able to climb a hill while in drive one day but be functional the next?

Is the shift linkage adjusted properly? It should be checked and adjusted whenever you have shifting problems, and whenever a transmission is replaced.

did you try Allison dealer

If it is a four wheel drive check your tail shaft or drive line by securing the vehicles front wheels jack up the rear tires and in park try to rotate the drive line if you can hear the transmission sound like it is going into gear the transfer case could be damaged! If not a four wheel drive pull the transmission dipstick and look to see if the fluid is dark red or metallic grayish color if so then you're clutch disks inside the tyranny have been worn out and it needs to be rebuilt!

Failed Transmission Again

Part with it

Get something else

Maybe American (Rear Wheel Drive Only)

4wd is best for wet or dirt roads. When on dry and the tires are not all the same wear size. You can and will break parts. Transfer case tends to break easy. Most times you should be in neutral to get it into low 4wd. The clunking your hearing when shifting from 2wd to 4wd is the transfer case and driveshafts coming unsprung from the extra torque of not having the same size tread tires. One tire been less then the other 3 can screw it up. May need to buy 4 new tires or just stay in two wheel drive unless you get stuck

Have codes read by someone with good scanner that reads trans codes.

Harmonic balancer.

What kinda batteries do you got? Are the cables any good? Sounds to me like a power/ground issuse. Either that or you have to small of batteries to crank over a high compession enigne when it's cold, with the glow plugs, and heater grid pulling all of the power from the batteries.
And check the trans fluid level for your problem with the trans.
And you're gonna need to be a little more specific on the thunping noise.

thawed it out the next morning-reset codes to standard-viola-all is well. seems ice found its way into switch@transfer case and ran the chips riot-sending tranny into limp mode. cold weather,rrrrrrrrrrrr. june can't come soon enough.
thanks anyway

the light is on.........let's see, where you having problems with clunking noises in the front, now or before when or not in 4 wheel drive? If so sounds like cv/axle shats/joints. Last time you used 4 wheel, was there a big clunk, just once? Is there an ocasional clunk when going over bumps? If so, sounds like Ujoint. I don't belive chevys use vaccum for 4 wheel drives systems at all.