had the same exact thing on my 87 ranger 2.9 the cats are full split it at the flange and pull the exhaust back should notice a differance right away other than being really loud. I chased mine for about 3 months finally found it when all it would do was idle
i have a similar problam my 87 ranger with a 2.9 i have replaced both the fuel pumps and filters and cleaned the injectors and it will run great 99% of the time but every now and then i will get in the truck in the morning and it will run like crap it dies at lights and coughs and smokes and the next day i will get in it and it runs great