Just get a new fuel pump. East to install and cheap to buy. Gotta do that next, ASAP. You can test as Martin says if you wish. In your case I would buy new.
bargabos - you were right! And thanks to all of you for the suggestions, and I know a few others thought it was the fuel pump too. Its wha I love the forums and the support and knowledge they offer.
So many issues threw me a curve ball, likely unrelated. So today I put on a new fuel pump. I'm glad I checked the rod also, as it was stuck in there with only slight movement but all the way back. I searched for advice and saw a few online have had this issue too. Thought I'd never get it out, but some very tight vise grips and a large crow bar for leverage finally broke it loose. I spent some time with the new rod (slightly longer too) oiling and cleaning to ensure it slipped in and out easily - took a while. Put the new pump on, made a new gasket and used some RTV and made sure it as sealed. Honestly the bolts seemed a little loose when I removed the original, so this one is on solid. Went for a test drive and its got more power than before and did not bog down once! Very happy.
The other, possibly unrelated issues; Low oil pressure. Could be a bad sender, or just how it is. The gauge has marks for 0 - 25 - 50 - 75 etc, so the distance between 0 - 25 is pretty small. I feel it goes super low and looks close to zero once its warm and at idle, but perhaps its still 5ish at idle. In any case I'll put a new sender and a new higher volume oil pump on next for reassurance. I did do a compression test before switching the fuel pump, and its between 165 - 170 in all cylinders! I did it cold, and didn't bother with a wet test, just happy to see they were all close. I'm not burning any oil, no bubbles in radiator. I still head the knock and lots of water came out the tailpipes. But with warmer weather and ran it a lot (and now actually had the real power and no hesitation - so its seems like its ok. Temp sitting at idle in the driveway for a while went to 200, but it seems happier and mostly stays close to the 180. I also have a 700R and spent a lot of time sorting out the shifting. Finally just went and bought the entire new bracket and cable and make it right. So with the bad fuel pump and bad shifting, and a little stress with finding quiet roads for tests - it was harder for me to work out what was going wrong.
I like to follow up once Ive found the solution or fixed the issue. I spend a lot of time searching the forums for help and hate it when I find someone with the same problem, and then after all the posts with options, the OP never comes back with the finale. So for me, it was mostly the fuel pump. It looked like it was new enough and clean, seemed to operate with the spring fine, and the rod I removed seemed straight, but replacing it all did the trick. Glad to have some summer cruising time and having a truck for some yard work in the future.
