Heavy Duty Mechanic Wanted

Looking for a mechanic with experience with older Hough payloaders. Not looking for someone to necessarily work on my machine but for someone who can tell me exactly what is wrong with it. It starts up and runs perfect, the bucket goes up and down, but when put into gear, the machine moves very slowly, even an inch at a time. When another vehicle pushes or pulls it, it seems to kick in and be a bit better but not perfect. Pretty sure the transmission is good, but believe its a torque converter problem or a valve is sticking or something else.

I’m offering up to $300 for an experienced mechanic to come to Starbuck and spend a couple hours with the machine to determine what is wrong. Not interested in mechanics with no experience with these machines or someone who is going to guess in the end what is wrong. I need to know exactly what I’m dealing with to get this machine working properly,

Its not the original engine in the machine, but a 2 cycle Detroit diesel with very low hours has been put in, but the engine doesn’t seem to be the problem as it starts and runs perfectly. Also I have changed all the fluids and filters hoping that may be the problem, but was not. Also not sure of the exact year of the machine, but its close to 1970.

The picture is not the actual machine but close