The blazer 4.3 4x4 shifts fine through all gears. But going up a hill it boggs down and will shift down to next lowest gear when it gets to 1st gear I have to pull over. If I turn it off and re start I can drive until it goes through this cycle of down shifting to 1st. All the time I'm climbing the hill the rpm's are up at 2 thousand, feels like I'm pulling a house behind me going up hills. Was running great on flat road now at around 40-50now it's starting to hesitate like the fuel pump is going bad but it was replaced 1-2 years a go. Did a scan and came up with a code for a bad shift solenoid . It shifts just as smooth as can be. I also had the transmission rebuilt 3 years a go. I'm at my wits end. Has new plugs, wires, distrbuter, Any help or suggestions would be greatly appreciated. Thanks too all in advance.