Transmission Not Shifting Past 2nd Gear

[tntitans21399]

I am sure there is a lot of post about this already, but I am new to this forum. I have a 1999 (classic 98 style) GMC C2500 truck that I got from my dad years ago when he passed. It was a work and personal truck. It has 298k on the truck. Original transmission. I'm not sure which transmission it is, i would guess the 4L80 type. Is the transmission for all the c2500 (5.7 Vortec) 4L80e?

Just replaced the engine 2 years ago around 288k. I upgraded to a new boat that weighs about 6,500lbs, 1,000lbs more than my last boat. Never had any issues hauling wood chips, trash, and the last boat. Didn't have issues when I first got the boat. The last 2 trips it seems to not want to shift past 2nd when towing. If I unhook from the boat it runs fine shifts good. When I went to the lake it shifted fine. But coming back home it went back to to only going in 1st and 2nd. Even going down a hill it doesn't want to shift. I can go 65mph but the rpms are real high. So I usually stay in the right lane and go about 55mph. I only drive 30 min to the lake. I have googled some and seems to be a 1-2 shift solenoid maybe. Would that act up only when towing and go away when empty?

 

[NickTransmissions]

I am sure there is a lot of post about this already, but I am new to this forum. I have a 1999 (classic 98 style) GMC C2500 truck that I got from my dad years ago when he passed. It was a work and personal truck. It has 298k on the truck. Original transmission. I'm not sure which transmission it is, i would guess the 4L80 type. Is the transmission for all the c2500 (5.7 Vortec) 4L80e?

Just replaced the engine 2 years ago around 288k. I upgraded to a new boat that weighs about 6,500lbs, 1,000lbs more than my last boat. Never had any issues hauling wood chips, trash, and the last boat. Didn't have issues when I first got the boat. The last 2 trips it seems to not want to shift past 2nd when towing. If I unhook from the boat it runs fine shifts good. When I went to the lake it shifted fine. But coming back home it went back to to only going in 1st and 2nd. Even going down a hill it doesn't want to shift. I can go 65mph but the rpms are real high. So I usually stay in the right lane and go about 55mph. I only drive 30 min to the lake. I have googled some and seems to be a 1-2 shift solenoid maybe. Would that act up only when towing and go away when empty?

Is it not upshifting at all or is it upshifting but feels like it's in neutral?

Any codes?

 

[tntitans21399]

Is it not upshifting at all or is it upshifting but feels like it's in neutral?

Any codes?

No codes.

When towing it doesn't shift up to 3rd. When I unhook the boat, it shifts normally. If you give it more gas it pulls more and the rpms raise it. It's not in neutral.

 

[movietvet]

No codes.

When towing it doesn't shift up to 3rd. When I unhook the boat, it shifts normally. If you give it more gas it pulls more and the rpms raise it. It's not in neutral.

"It's not in neutral".

I believe he asked if it "felt like it was in neutral". @NickTransmissions is asking the question that way for a reason. I am not a transmission guy but I like to read in when @NickTransmissions is involved and he asks questions for a reason.

Honest mistake.

 

[NickTransmissions]

No codes.

When towing it doesn't shift up to 3rd. When I unhook the boat, it shifts normally. If you give it more gas it pulls more and the rpms raise it. It's not in neutral.

Gotcha...When you're towing, are you activating the 'Tow Mode' feature (on the GMT800s, it's a button on the column shifter, not sure where it is on the GMT400s)?

Plug in your scan tool, bring up the live transmission data, take for a test drive while towing and see if the PCM is commanding an upshift into 3rd; let us know.

 

[tntitans21399]

"It's not in neutral".

I believe he asked if it "felt like it was in neutral". @NickTransmissions is asking the question that way for a reason. I am not a transmission guy but I like to read in when @NickTransmissions is involved and he asks questions for a reason.

Honest mistake.

No it doesn't feel like it is in neutral. Just not going to 3rd for more speed and less rpm's.

 

[tntitans21399]

"It's not in neutral".

I believe he asked if it "felt like it was in neutral". @NickTransmissions is asking the question that way for a reason. I am not a transmission guy but I like to read in when @NickTransmissions is involved and he asks questions for a reason.

Honest mistake.

On my truck their isn't a tow/haul button. Just shifter, 1, 2, 3, D(with circle for overdrive).

 

[tntitans21399]

Why would it only act that way when towing? If I drive the truck empty it shifts normal and acts normal. The previous boat I had (about 5,000lbs) didn't have any issues.