deadhead813

My 89 (5.0 litre). Dual tanks with new pump on the rail. New filter. New fuel pressure regulator. When I say new 1 yr 4000 miles ago Had all pumps pressure-checked last August. All within spec. When air temp gets above 75 or so, damned thing will stall going down the road at 55. Hard to start afterwards. Seven stalls in last 4 miles coming home this afternoon. Hard starting afterwards. Eventually starts, good for 1/2 mile or so. Any ideas? Where do I start? Thanks in advance for any help!!!