can't figure out the puzzel

First thing to look at, have you impeded the flow of air at the intake or through the cooker in any way.

Your charcoal basket is the problem. The fuel is packed to tight and it is taking up needed air space needed to achieve higher temps. Off sets are all about flow the less restriction the better. To illustrate this think about a funnel in a bottle neck. If you pour water in the funnel it enters the bottle at a even pace, now if you put a paper towel in the funnel and pour the same amount of water it will take twice as long to fill the bottle. If the funnel represents the fire box, the bottle the oven of your smoker, the water the heat & smoke and the paper towel the charcoal basket it all make sense.
They are called stick burners for a very good reason they are designed to burn wood not charcoal. They are meant for hands on cooking. Just like a Harley or a Hot rod they need a little tinkering on a regular basis to run at peak performance unlike the mom mobile that only needs some gas and light infrequent maintenance. If you want long burn times and mostly hands off sell it and buy a WSM or buy a bigger cooler, pull up a comfy chair next to the wood pile and a good book to pass the time.

Small Hot fire fed often.

I went through the same problem with my old offset and like others mentioned, it was the charcoal basket causing my issues. With expanded metal and any fuel besides wood I had to briskly shake the basket regularly to drop the ash and keep it from suffocating the fire. Later on I just used an old grill grate that i made fit in the firebox. Things worked much better for me once I ditched the expanded metal.

agree with the basket comments

I have an Ok Joe also but its a bit different since I dont have the ash pan

If yours is anything like mine you have a 3 fire grates, 2 in the smoke chamber and 1 in the firebox

what I did was take the firebox grate and turn it 90 degrees, this sets it up higher in the firebox.

Slide it to one side of the box and take one of the other grates from the smoke chamber and set it next to it. They fit side by side this way perfectly

Try that and see if you have better air flow. I have no problems getting mine to 375f. I also have found that the best airflow is closest to the cooking chamber side of the firebox, so I build my fire there.

I start with charcoal for a bed then use sticks.

+1 on using the grates to raise the level of the basket. Worked great for me when I had an OK Joe. You mentioned a sheet metal ash pan. You don't have your basket sitting directly on the sheet metal do you? That would restrict airflow.

I get that stick burners are for sticks. But some of these ok joes depending on what you have are better hybrids. I used a basket on my old one with a heat deflector and had even temps at four hour clips.

Post some pics if you have them.

that height looks fine

you do clean that out after each smoke dont you?

That looks like it should work, when I made my charcoal basket for my UDS, I put four 3" bolts with some nuts and washers for legs to keep it off the bottom.

I have the new OK Joe. I made my basket 14x14x8. It works just fine, ive found that if I close off the intake and open the stack to about 1/2 to 1/4 it holds temps around 275 to 300 with lump. I also use the minion method in the basket.