Hey guys, new member here. Have an 84 flat bed ranger with a pretty odd issue. Runs great for about 45 minutes of 65mph+ driving. After that it starts missing. If I slow down to about 40mph it will usually correct itself and run normal for a few miles but then start again. Now it will still maintain speed but it is defiently misfiring on atleast on one cylinder. I have shut it down while this has happened and then checked for spray from accelerator pump to try to rule out vapor lock. It does spray but I havent totally ruled out a vapor lock scenario but does seem unlikely. If i keep it under 60mph I can drive all day no issues. Now more about the truck. 2.8l v6 not orginal to this truck. I swapped this motor in about 4 months ago and this is when the issues started. From what I was told motor came out of a B2 and was a ford reman unit. It does have the reman sticker and before i installed the engine pulled rod cap and main cap. Both were .010 under and pistons were .040 over so seems to make sense it was a reman. I resealed the engine along with stage 2 cam,stiffer valve springs,remaned heads. Truck has been converted to duraspark 2 running a non feedback 2150 carb. New dspark box, distriubutor, cap and rotor plugs, plug wires fuel pump and fuel lines. Dropped the tank and its clean and venting. New fuel lined from tank to pump and wrapped in heat resistant sheilding where it gets close to exhaust. The only “weird” thing I have found is base timing is set at 12 btdc. Now she will run there but doesnt sound too happy. She sounds better at about 25 btdc. I have set it to 12 because with with the mechanical and vaccum full in if it was set to 25 the timing would be almost 50 which seems like alot for this motor. My old 2.8 was set at 12 btdc and seemed happy there.I have also tested this issue with diffrent base timings and with the vaccum advance plugged and did not make a diffrence, however thought it was odd enough to add it here. I have replaced almost everything related to fuel and ignition in an attempt to fix this issue but I am at a loss and running out of money and ideas. Any help would be greatlyappreciated. I apologize for the long winded first post but wanted to make sure I gave as much info as I could. Thanks again!