My 5.0 with 3.73s did a great job pulling my 5500 lb dry/ 7500 lb gross trailer over Snoqualmie Pass on I90 in WA today. Trailer is probably loaded to around 6800 lbs today since it brought a full load of water. It's not a real daunting grade but I was impressed how well it did and held 63 mph in 4th gear around 3000 rpm or 3rd gear around 3800 rpm depending on how steep the grade was. It even held 5th gear on some lesser grades more than i thought it would. I lock out 6th gear when towing since it won't use it much. It could accelerate at any time if I needed it to and it sounds great doing it IMHO.
I wouldn't expect the 3.55s would be massively worse, but can't say for sure.